JP2009211188A - Memory system - Google Patents

Abstract

To provide a memory system capable of improving the reliability of data restoration while storing snapshots and logs in a NAND flash memory using multi-valued memory cells.
A volatile first storage unit, a non-volatile second storage unit and a management information including a storage position of data stored in the second storage unit as well as data transfer with the first storage unit. And a controller that performs data management in the first and second storage units while updating the management information, and the second storage unit is management information of the first storage unit Log storage blocks 41, 42 that store a snapshot, a log 220 that is update difference information of management information, and a second pointer 230 that indicates a storage position of the snapshot and the log 220 and constitute a log storage area of the log 220. On the other hand, the log storage block 41 has a pointer indicating the position of the log storage block 42.
[Selection] FIG.

Description

  The present invention relates to a memory system configured using a nonvolatile semiconductor memory device.

  In a personal computer using a hard disk device as a secondary storage device, a technique for taking a backup in order to prevent data stored in the hard disk device from becoming invalid data due to some trouble is known. For example, when a change in data in the hard disk device is detected, a snapshot which is a backup copy before the change of the data is taken, and a log in which updates to the data are recorded is taken. Thereafter, a process of taking a snapshot every predetermined time, invalidating a past log before taking the snapshot, and generating a new log is repeatedly performed (for example, see Patent Document 1). If the data becomes invalid, the data can be restored based on the snapshot and the log.

  In recent years, the capacity of NAND flash memories, which are nonvolatile semiconductor memory devices, has been increased, and personal computers using a memory system having the NAND flash memory as a secondary storage device have been commercialized. However, in contrast to backup of data stored in a personal computer having such a NAND flash memory as a secondary storage device, backup of data stored in a personal computer having a hard disk device as a secondary storage device; Similarly, the technique of Patent Document 1 cannot be applied. This is because, in order to increase the capacity of the NAND flash memory, a multi-level memory technology capable of storing a plurality of data (multi-level data) of 2 bits or more in one memory cell is used.

  A memory cell constituting a multi-value memory has a field effect transistor structure having a stacked gate structure in which a gate insulating film, a floating gate electrode, an inter-gate insulating film, and a control gate electrode are sequentially stacked on a channel region. A plurality of threshold voltages can be set according to the number of electrons accumulated in the gate electrode. In order to enable multi-value storage using the plurality of threshold voltages, it is necessary to control the distribution of threshold voltages corresponding to one data very narrowly.

  For example, in a multilevel memory capable of storing four values, two bits (four values) are stored by providing a lower page and an upper page in one memory cell and writing 1-bit data in each page. There is something. In such a multi-level memory data writing method, data is written to the lower page of the first memory cell, and then the data is written to the lower page of the adjacent memory cell (second memory cell). Then, after writing to the adjacent memory cell, data is written to the upper page of the first memory cell (see, for example, Patent Document 2).

  However, in such a multi-level memory, the threshold voltage of the memory cell written earlier is adjacent to the memory cell and fluctuates depending on the threshold voltage of the memory cell written later. For this reason, in multi-level memory, if writing is interrupted, for example, due to an abnormal shutdown of the power supply during the writing of the upper page of a certain memory cell, lower page data destruction that destroys the data of the lower page that has been written first will occur. It can happen.

  In a memory system having a NAND flash memory, when data is stored, it is necessary to erase a write area once in a unit called a block, for example, and then write in a unit called a page. On the other hand, there is a problem in that the deterioration of memory cells constituting the block proceeds as the number of block erasures performed prior to such data writing increases. Therefore, in a personal computer using a NAND flash memory as a secondary storage device, it is necessary to perform data management for suppressing the number of block erasures, and when restoring data based on the snapshot and log described above. However, it is necessary to perform data management so as to suppress the number of block erases.

US Patent Application Publication No. 2006/0224636 JP 2004-192789 A

  The present invention has been made in view of the above, and is a memory system capable of improving the reliability of data restoration while storing snapshots and logs in a NAND flash memory using multi-valued memory cells. The purpose is to provide.

  According to one aspect of the present invention, a volatile first storage unit, a nonvolatile second storage unit composed of memory cells capable of storing multi-value data, and a host via the first storage unit Performing data transfer between the device and the second storage unit, taking management information including the storage location of the data stored in the second storage unit at startup into the first storage unit, A controller that manages data in the first and second storage units based on management information while updating the captured management information, and the second storage unit is configured when a predetermined condition is satisfied. A log that stores a snapshot storage area that is acquired and stores a snapshot that is the management information of the first storage unit, and a log that is difference information before and after the change when the management information is changed Storage space and A pointer storage area for storing a first pointer indicating a storage position of the snapshot storage area and the log storage area, and the log storage area erases data according to the size of the log to be stored It is configured by sequentially securing blocks as units, and the block has a second pointer indicating the position of the next secured block.

  According to another aspect of the present invention, a volatile first storage unit, a nonvolatile second storage unit composed of memory cells capable of storing multivalued data, and the first storage unit In addition to transferring data between the host device and the second storage unit, the management information including the storage location of the data stored in the second storage unit at the time of startup is taken into the first storage unit A controller for managing data in the first and second storage units based on the management information while updating the fetched management information, wherein the second storage unit satisfies a predetermined condition A snapshot storage area for storing a snapshot that is the management information in the first storage unit and a log that is difference information before and after the change when the management information is changed Log storage area And a pointer storage area for storing a first pointer indicating a storage position of the snapshot storage area, and the log storage area is a data erasure unit according to the size of the log to be saved The second pointer indicating the storage location of the first log stored in the log storage area is stored in the snapshot, and the block is the position of the next allocated block. It has the 3rd pointer which shows.

  According to still another aspect of the present invention, a volatile first storage unit, a nonvolatile second storage unit composed of memory cells capable of storing multi-value data, and the first storage unit Data is transferred between the host device and the second storage unit via the network, and management information including the storage location of the data stored in the second storage unit at the time of activation is stored in the first storage unit. A controller that manages data in the first and second storage units based on management information while updating the captured management information, and the second storage unit is changed to the management information A log storage area that stores a log that is difference information before and after the change when the error occurs, and a snapshot storage area that stores a snapshot that is the management information of the first storage unit, and The controller When grayed storage area is full of logs, and the log storage area acquires the snapshot when it becomes defective region can not be data storage, characterized in that stored in the snapshot storage area.

  According to the present invention, there is an effect that reliability of data restoration can be improved by multiplexing points indicating log storage positions.

  Embodiments of a memory system and management information storage method according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to these embodiments.

(Embodiment)
This memory system includes a nonvolatile semiconductor memory device, and is used as a secondary storage device (SSD: Solid State Drive) of a host device such as a personal computer, for example, and stores data for which a write request is issued from the host device. In addition, it has a function of reading data requested to be read from the host device and outputting it to the host device. FIG. 1 is a block diagram showing an example of the configuration of the memory system according to the first embodiment of the present invention. The memory system 10 includes a DRAM (Dynamic Random Access Memory) 11 as a first storage unit, a NAND flash memory (hereinafter referred to as a NAND memory) 12 as a second storage unit, a power supply circuit 13, and a drive. And a control unit 14.

  The DRAM 11 is used as a storage unit for data transfer, management information recording, or work area. Specifically, as a storage unit for data transfer, data requested to be written from the host device is temporarily stored before being written to the NAND memory 12, or data requested to be read from the host device is NANDed. It is used for reading out from the memory 12 and temporarily storing it. The management information recording storage unit is used to store management information for managing the storage location of data stored in the DRAM 11 and the NAND memory 12. Furthermore, the storage unit for the work area is used at the time of expansion of the before and after logs (previous log and subsequent log) used when restoring the management information.

  The NAND memory 12 is used as a storage unit for storing data. Specifically, data designated by the host device side is stored, or management information managed by the DRAM 11 is stored for backup. FIG. 1 shows a case where the NAND memory 12 is configured by four channels 120A to 120D. One channel 120A to 120D includes two packages 121 in which eight chips 122 having a storage capacity of a predetermined size are combined into one. Each channel 120 </ b> A to 120 </ b> D is connected to the drive control unit 14 via the bus 15.

  The power supply circuit 13 receives an external power supply and generates a plurality of internal power supplies to be supplied to each part of the memory system 10 using the external power supply. The power supply circuit 13 detects the rise or fall of the external power supply and generates a power-on reset signal. This power-on reset signal is sent to the drive control unit 14.

  The drive control unit 14 controls the DRAM 11 and the NAND memory 12. Although details will be described later, for example, in accordance with a power-on reset signal from the power supply circuit 13, management information restoration processing and management information storage processing are performed. Further, the drive control unit 14 transmits / receives data to / from the host device via the ATA interface (denoted as ATA I / F in the figure), and the RS232C interface (denoted as RS232C I / F in the figure). ) To send / receive data to / from the debugging device. Further, the drive control unit 14 outputs a control signal for controlling a status display LED provided outside the memory system 10.

  Here, the configuration of the NAND memory 12 will be described. The NAND memory 12 is configured by arranging a plurality of blocks (erase unit areas), which are units of data erase, on a substrate. FIG. 2 is a circuit diagram showing an example of the configuration of one block included in the NAND memory. In FIG. 2, the left-right direction on the paper surface is the X direction, and the direction perpendicular to the X direction on the paper surface is the Y direction.

  Each block BLK of the NAND memory 12 includes (m + 1) (m is an integer of 0 or more) NAND strings NS arranged in order along the X direction. Each NAND string NS has (n + 1) (n is an integer of 0 or more) connected in series in the Y direction sharing a diffusion region (source region or drain region) between memory cell transistors MT adjacent in the Y direction. Memory cell transistors MT0 to MTn and select transistors ST1 and ST2 arranged at both ends of the column of (n + 1) memory cell transistors MT0 to MTn.

  Each of the memory cell transistors MT0 to MTn is composed of a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) having a stacked gate structure formed on a semiconductor substrate. Here, in the stacked gate structure, the charge storage layer (floating gate electrode) formed on the semiconductor substrate with the gate insulating film interposed therebetween, and the inter-gate insulating film on the charge storage layer was formed. A control gate electrode. The memory cell transistors MT0 to MTn are multi-value memories that can store data of 2 bits or more according to a difference in threshold voltage depending on the number of electrons stored in the floating gate electrode. . In the embodiment described below, the case where the memory cell transistor MT is a multilevel memory will be described as an example.

  Word lines WL0 to WLn are connected to the control gate electrodes of the memory cell transistors MT0 to MTn constituting the NAND string NS, respectively, and between the memory cell transistors MTi (i = 0 to n) in each NAND string NS. Are commonly connected by the same word line WLi (i = 0 to n). That is, the control gate electrodes of the memory cell transistors MTi in the same row in the block BLK are connected to the same word line WLi. A group of (m + 1) memory cell transistors MTi connected to the same word line WLi is a unit constituting one page. In the NAND memory 12, data is written and read in units of pages.

  Bit lines BL0 to BLm are connected to the drains of (m + 1) selection transistors ST1 in one block BLK, respectively, and a selection gate line SGD is commonly connected to the gates. The source of the select transistor ST1 is connected to the drain of the memory cell transistor MT0. Similarly, a source line SL is commonly connected to sources of (m + 1) selection transistors ST2 in one block BLK, and a selection gate line SGS is commonly connected to gates. The drain of the select transistor ST2 is connected to the source of the memory cell transistor MTn.

  Although not shown, the bit line BLj (j = 0 to m) in one block BLK is connected to the drain of the selection transistor ST1 in common with the bit line BLj of another block BLK. Yes. That is, the NAND strings NS in the same column in the plurality of blocks BLK are connected by the same bit line BLj.

  Next, functional configurations of the DRAM 11 and the NAND memory 12 will be described. FIG. 3 is a diagram schematically illustrating the functional configuration of the DRAM and the NAND memory. FIG. 3A illustrates the functional configuration of the DRAM 11, and FIG. 3B illustrates the functional configuration of the NAND memory 12.

  As shown in FIG. 3A, the DRAM 11 includes a write cache area WC that stores data requested to be written from the host apparatus, and a read cache area that stores data requested to be read from the host apparatus. RC, temporary storage area 111 in which management information for managing the storage location of data stored in DRAM 11 and NAND memory 12 is stored, and work area 112 used when restoring the management information .

  As illustrated in FIG. 3B, the NAND memory 12 stores management information managed in the data storage area 125 in which data requested to be written from the host device is stored and the temporary storage area 111 in the DRAM 11. Management information storage area 126. In this example, the data write / read unit in the NAND memory 12 is a page size unit, and the erase unit is a block size unit (for example, 512 KB unit). For this reason, an area for storing each block of the NAND memory 12 managed in block size units is further divided into areas in page size units.

  Here, management information managed in the temporary storage area 111 of the DRAM 11 will be described. FIG. 4 is a diagram illustrating an example of a layer structure for managing data stored in the memory system. Here, the data refers to data that has been requested to be written / read from the host device. In this memory system 10, a DRAM management layer 31 that performs data management in the DRAM 11 that serves as a cache, a logical NAND management layer 32 that performs logical data management in the NAND memory 12, and a physical in the NAND memory 12. Data management is performed in a three-layer structure of a physical NAND management layer 33 that performs simple data management and life extension processing of the NAND memory 12.

  In the write cache area WC and the read cache area RC of the DRAM 11, data specified by a logical address (hereinafter referred to as LBA (Logical Block Address)) managed by the address management method of the host device is within a predetermined range on the DRAM 11. It is stored in a physical address (hereinafter referred to as a physical address in DRAM). The data in the DRAM management layer 31 includes cache management information 41 including a correspondence between the LBA of stored data and a physical address in the DRAM, and a sector flag indicating the presence / absence of data in the sector size unit in the page. Managed by.

  FIG. 5 is a diagram illustrating an example of the cache management information table. Here, the cache management information 41 has one entry for one page size area of the DRAM 11 and the number of entries is equal to or less than the number of pages that can be stored in the write cache area WC and the read cache area RC. Each entry is associated with an LBA of page size data, a physical address in DRAM, and a sector flag indicating the position of valid data in each area obtained by dividing the page by the sector size.

  In the NAND memory 12, data from the DRAM 11 is stored in a predetermined range of physical addresses (hereinafter referred to as “in-NAND physical addresses”) on the NAND memory 12. Further, in the NAND memory 12 composed of a multi-value memory, the number of rewritable times is limited, and therefore, the drive control unit 14 controls the number of times of rewriting between the blocks constituting the NAND memory 12 to be equalized. That is, when updating the data written to a physical address in a NAND in the NAND memory 12, the drive control unit 14 reflects data that reflects a portion that needs to be updated in a block including the data. Control is performed so that the number of rewrites between the blocks constituting the NAND memory 12 is equalized by writing to a block different from the original block and invalidating the original block.

  As described above, in the NAND memory 12, the processing unit is different between the data write / read process and the erase process, and in the data update process, the data position (block) before the update and the data position after the update are updated. In this embodiment, in addition to the physical address in the NAND, a logical address in the NAND (hereinafter referred to as a logical address in the NAND) that is uniquely used in the NAND memory 12 is provided in this embodiment.

  Therefore, the data in the logical NAND management layer 32 is between the LBA of the page size unit data received from the DRAM 11 and the logical address in the NAND indicating the logical page position of the NAND memory 12 storing the received data. And logical NAND management information 42 indicating a relationship indicating the address range of a logical block (hereinafter referred to as a logical block) having the same size as the erase unit block in the NAND memory 12. Note that a plurality of logical blocks may be combined into a logical block. Further, data in the physical NAND management layer 33 includes NAND logical address-physical address conversion information (hereinafter referred to as logical-physical conversion information) 43 including the correspondence between the logical addresses in the NAND and the physical addresses in the NAND memory 12. Managed by.

  FIG. 6 is a diagram illustrating an example of a logical NAND management information table, and FIG. 7 is a diagram illustrating an example of a NAND intrinsic-physical conversion information table. As shown in FIG. 6, the logical NAND management information 42 includes logical page management information 42a and logical block management information 42b. The logical page management information 42a has one entry for one logical area of one page size, and each entry has an LBA of data of one page size, a logical address in NAND, and whether this page is valid. And a page flag indicating that. Further, the logical block management information 42b includes a physical address in the NAND set for an area of one block size in the NAND memory 12. Further, as shown in FIG. 7, in the NAND intrinsic / physical conversion information 43, the NAND physical address and the NAND logical address of the NAND memory 12 are associated with each other.

  With these management information, the LBA used in the host device, the logical address in the NAND used in the NAND memory 12, and the physical address in the NAND used in the NAND memory 12 can be associated with each other. And the memory system 10 can exchange data.

  In the following, the management information managed by the DRAM management layer 31 is lost when the power is turned off. Therefore, it is also referred to as a volatile table. The management information managed by the logical NAND management layer 32 and the physical NAND management layer 33 is: When the memory system 10 disappears due to power-off or the like, it is necessary to store and save the memory system 10 next time, so it is also called a non-volatile table.

  This non-volatile table manages the data stored in the NAND memory 12, and without this non-volatile table, the information stored in the NAND memory 12 cannot be accessed, or in the area already stored. Since data is erased, it is necessary to save the latest information in preparation for unexpected power off. Therefore, in this embodiment, management information including at least a nonvolatile table is stored in the management information storage area 126 of the NAND memory 12 in the latest state. Next, management information storage information stored in the management information storage area 126 of the NAND memory 12 will be described. Hereinafter, a case where only the nonvolatile table is stored in the management information storage area 126 will be described as an example.

  FIG. 8 is a diagram schematically illustrating an example of the contents of management information storage information stored in the management information storage area. In this management information storage area 126, the snapshot 210 which is the contents of the nonvolatile table at a certain point in time and the update difference information of the contents of the nonvolatile table until the next snapshot is taken and acquired before the update The pre-update log (hereinafter referred to as the pre-log) 220A, the post-update log (hereinafter referred to as the post-log) 220B having the same contents as the previous log 220A and saved after the update, and the position of the snapshot 210 (Block), a second pointer 230 indicating the position (block) of the previous log 220A acquired for this snapshot 210, and the position (block) of the subsequent log 220B acquired for this snapshot 210, and a second Root pointer indicating the position (block) where the pointer 230 is stored Management information storage information including a 40, a is stored. Here, the snapshot 210 refers to information in which management information including at least a nonvolatile table is stored at a predetermined time among management information stored in the temporary storage area 111 of the DRAM 11.

  In FIG. 8, the snapshot 210, the previous log 220A, the rear log 220B, the second pointer 230, and the root pointer 240 are stored in different blocks. Also, the size of these blocks is the same size as the physical block which is an erasing unit. The snapshot 210 is stored in a snapshot storage block. The snapshot 210 includes logical NAND management information 42 that is a nonvolatile table in the management information storage area 126 of the NAND memory 12 and NAND intrinsic / physical conversion information 43. When the new snapshot 210 is saved, it is saved in a different block from the previously saved snapshot 210.

  The pre-log 220A and the post-log 220B are the non-volatile table and the snapshot 210 (or the log already taken with the snapshot 210) after the content update when the content of the non-volatile table is changed due to the data writing process or the like. Difference information. Specifically, the first previous log 220 </ b> A or the first subsequent log 220 </ b> B after the snapshot 210 is taken is difference information between the nonvolatile table and the snapshot 210. Further, the second and subsequent previous logs 220A after the snapshot 210 is taken are difference information between the non-volatile table and the combination of the previous log 220A and the snapshot 210 that have already been taken. Further, the second and subsequent post-logs 220B after the snapshot 210 is taken are difference information between the non-volatile table and the combination of the post-log 220B and the snapshot 210 that have already been taken.

  The previous log 220A is information generated before the management information is actually updated. Therefore, before the management information is actually updated by performing a data writing process or the like, the previous log 220A is generated based on the update plan of how the management information is updated. The post log 220B is information generated after the management information is actually updated. Therefore, after the management information is actually updated by performing a data write process or the like, the post-log 220B is generated using the actual management information.

  The pre-log 220A and the post-log 220B are each stored in a log storage block. The front log 220A and the rear log 220B are added to the same log storage block even if the snapshot generation changes.

  FIG. 9 is a diagram illustrating an example of a log. Since the previous log 220A and the subsequent log 220B have the same information, the previous log 220A will be described as an example of the log here. The log 220A includes target information that is management information to be changed, a target entry that is an entry to be changed in the target information, a target item that is an item to be changed in the target entry, and the target item. And the change content that is the content of the change. Since the previous log 220 </ b> A and the subsequent log 220 </ b> B are update difference information with respect to the snapshot 210, it is renewed when the new snapshot 210 is saved.

  The second pointer 230 is stored in the second pointer storage block. The second pointer 230 only needs to indicate the head address of the block indicating the storage position of the snapshot 210, the previous log 220A, and the subsequent log 220B. The second pointer 230 is updated when the snapshot 210 is newly saved or when the snapshot storage block and the log storage block are changed.

  The second pointer 230 stores snapshot access information for accessing the snapshot storage block, log access information for accessing each log storage block of the previous log 220A and the subsequent log 220B, and the next second pointer. A next pointer indicating a page position to be displayed. By this next pointer, the second pointer 230 becomes linked list type information, and by following the next pointer from the first page of the second pointer storage block designated by the root pointer 240, it is possible to reach the latest second pointer 230. It becomes possible. Instead of the linked list method, the second pointer 230 may be additionally stored in order from the first page of the second pointer storage block.

  The root pointer 240 is stored in a root pointer storage block. The root pointer 240 is information for accessing the second pointer storage block in which the second pointer 230 is stored, and is initially read at the time of the processing for restoring the management information when the memory system 10 is activated. It is. The root pointer 240 is changed when the second pointer storage block is changed. The root pointer 240 is additionally stored in the root pointer storage block, for example, sequentially from the first page of the block. In such a case, the page immediately before the unwritten page in the root pointer storage block has the latest information, so by searching the top page of the unwritten page, the latest page is obtained. The route pointer 240 can be retrieved. Further, as in the case of the second pointer 230, a linked list method can also be used.

  Here, the root pointer 240 is stored in the fixed area 1261 in the NAND memory 12, and the snapshot 210, the previous log 220 </ b> A, the subsequent log 220 </ b> B, and the second pointer 230 are stored in the variable area 1262 in the NAND memory 12. The fixed area 1261 is a protection area in which the relationship between the logical block managed by the logical NAND management layer 32 and the physical block managed by the physical NAND management layer 33 is fixed in the NAND memory. This is an area in which information necessary for operating the memory system 10 is stored.

  One variable area 1262 is an area of the NAND memory 12 excluding the fixed area 1261, and the relationship between the logical block managed by the logical NAND management layer 32 and the physical block managed by the physical NAND management layer 33 is variable. This is an area that is a target of wear leveling.

  Next, functions of the drive control unit 14 will be described. FIG. 10 is a block diagram illustrating an example of a functional configuration of the drive control unit. The drive control unit 14 cooperates with the data management unit 141 that performs data transfer between the DRAM 11 and the NAND memory 12 and controls various functions related to the NAND memory 12, and the data management unit 141 based on instructions received from the ATA interface. An ATA command processing unit 142 that performs data transfer processing, a security management unit 143 that manages various types of security information in cooperation with the data management unit 141 and the ATA command processing unit 142, and each management program (FW) when the power is turned on. From the NAND memory 12 to a memory (not shown) (for example, SRAM (Static RAM)), an initialization management unit 145 for initializing each controller and circuit in the drive control unit 14, and an RS232C interface from the outside Deva supplied through It includes a debug support unit 146 processes the grayed for data.

  FIG. 11 is a block diagram illustrating an example of a functional configuration of the data management unit according to the present embodiment. The data management unit 141 is a data transfer processing unit 151 that transfers data between the DRAM 11 and the NAND memory 12, and a management that changes or saves management information in accordance with changes in data stored in the DRAM 11 and the NAND memory 12. An information management unit 152 and a management information restoration unit 155 that restores the latest management information based on the management information saved when the power is turned on or the like are further provided.

  The management information management unit 152 further includes a management information writing unit 153 and a management information storage unit 154. The management information writing unit 153 updates the management information stored in the DRAM 11 when the data transfer processing unit 151 needs to update the management information by changing the data stored in the DRAM 11 or the NAND memory 12. .

  When the memory system 10 satisfies a predetermined condition, the management information storage unit 154 updates the management information as the snapshot 210 and the updated information in the management information as the previous log 220A. Minute information is stored in the management information storage area 126 of the NAND memory 12 as a post log 220B. In addition, when the position where the second pointer 230 is written is changed with the saving of the snapshot 210, the previous log 220A, or the subsequent log 220B, the second pointer 230 is also updated.

The storage of the snapshot 210 by the management information storage unit 154 is executed when any one of the following three snapshot storage conditions is satisfied.
(1) Standby (instruction to reduce the power consumption of the main body of the memory system 10 to the minimum) / sleep (instruction to stop the device when there is no access for a predetermined time) / reset (restart the memory system 10) When receiving instructions).
(2) When the log storage area provided for storing the previous log 220A and the subsequent log 220B in the management information storage area 126 of the NAND memory 12 is filled.
(3) The log storage area provided for storing the previous log 220A and the subsequent log 220B in the management information storage area 126 of the NAND memory 12 becomes a defective area (bad block) where data cannot be written or erased. If

  The timing at which the management information storage unit 154 stores the previous log 220A and the subsequent log 220B is when the management information (nonvolatile table) stored in the DRAM 11 is updated by the management information writing unit 153. . Specifically, the pre-log 220A and the post-log 220B are saved before and after the process of writing data and the like.

  When the memory system 10 is powered on, the management information restoration unit 155 performs management information restoration processing based on the management information storage information stored in the management information storage area 126 of the NAND memory 12. Specifically, the root pointer 240 in the fixed area 1261, the second pointer 230 in the variable area 1262, the snapshot 210, the previous log 220 </ b> A, and the rear log 220 </ b> B are sequentially traced to the previous snapshot 210. It is determined whether or not the log 220A and the post log 220B exist. When the previous log 220A and the subsequent log 220B do not exist, the snapshot 210 of the snapshot storage block is restored to the DRAM 11 as management information. In addition, when the previous log 220A and the subsequent log 220B exist, it is a case of abnormal termination such as a program error or a momentary interruption (power supply interruption), so the snapshot 210 is acquired from the snapshot storage block. Then, the previous log 220A or the subsequent log 220B is acquired from the log storage block, and the management information (nonvolatile table) is restored by reflecting the previous log 220A or the subsequent log 220B in the snapshot 210 on the DRAM 11.

  Here, a process of storing management information of the memory system 10 by the management information management unit 152 will be described. FIG. 12 is a flowchart illustrating an example of a storage system management information storage processing procedure. FIG. 13 is a diagram for explaining pre-log and post-log storage processing. Here, the memory system 10 is connected to the host device and operates as a secondary storage device of the host device, and the host device (memory system 10) is in an activated state. It is assumed that the snapshot 210 is saved before the memory system 10 is stopped.

  First, the host device (memory system 10) is activated based on the snapshot 210 saved when the host device (memory system 10) ended last time (step S11). Thereafter, data reading / writing is performed from the host device to the NAND memory 12 as necessary. The management information management unit 152 determines whether or not the snapshot storage condition is satisfied (step S12). If the snapshot saving condition is not satisfied (No in step S12), it is determined whether or not an instruction accompanied by an update of management information (such as an instruction to write data to the NAND memory) has been received (step S13). If no instruction accompanying management information update is received (No in step S13), the process returns to step S12.

  In addition, when an instruction accompanied by an update of management information is received (Yes in step S13), an update plan is determined as to how the management information is updated by executing the instruction (step S14). The update plan is stored as the previous log 220A in the log storage block of the management information storage area 126 of the NAND memory 12 (step S15).

  In the update plan (previous log), when the previous log 220A is not stored in the log storage block, the snapshot stored in the nonvolatile storage table and the snapshot storage block when the management information is updated 210, when the previous log 220A (hereinafter referred to as the previous previous log 220A) has already been stored in the log storage block, and the non-volatile table when the management information is updated The difference information between the snapshot 210 and the previous previous log 220A. Specifically, as shown in FIG. 13, before the data write (X) is performed as the X-th data write process, the previous log (X) corresponding to the data write (X) is stored in the NAND memory 12. It is stored as the previous log 220A. At this time, for example, information y1 is stored as the previous log 220A. The previous log 220A here is stored in the management information storage area 126 of the NAND memory 12 after the previous log 220A (update plan) is recorded on the DRAM 11, for example.

  Next, the logical NAND management layer executes the instruction received in step S13 (for example, writing (X) processing of user data to the data storage area 125 of the NAND memory 12) (step S16).

  Thereafter, the management information stored in the DRAM 11 is updated according to the executed processing. Then, the management information storage unit 154 stores the updated information in the management information in the management information storage area 126 of the NAND memory 12 as a post log 220B. Here, the post-log 220B is the difference information between the current non-volatile table and the snapshot 210 stored in the snapshot storage block when the post-log 220B is not stored in the log storage block. If the later log 220B (hereinafter referred to as the past later log 220B) has already been stored in the log storage block, the current nonvolatile table, the snapshot 210 and the past log are combined. Is the difference information.

  As a result, the post-log 220B (X) corresponding to the data write (X) is stored in the NAND memory 12 as the post-log 220B (step S17). At this time, for example, information y1 is stored as the post log 220B. Thus, the information y1 stored as the post-log 220B is the same information as the information y1 stored as the pre-log 220A. Then, it returns to step S12.

  If the snapshot saving condition is not satisfied (No in step S12) and if an instruction accompanied by an update of management information is received (Yes in step S13), the processes of steps S14 to S17 are performed. It is. That is, the (X + 1) th data write process is performed in the same manner as the Xth data write process. At this time, before performing data writing (X + 1) as the (X + 1) -th data writing process, the previous log (X + 1) corresponding to this data writing (X + 1) is stored in the NAND memory 12 as the previous log 220A. . At this time, for example, information y2 is stored as the previous log 220A. Then, data is written (X + 1) to the data storage area 125 in the NAND memory 12. Further, the post log (X + 1) corresponding to the data write (X + 1) is stored in the NAND memory 12 as the post log 220B. At this time, for example, information y2 is stored as the post-log 220B. As described above, the information y2 stored as the post-log 220B is the same information as the information y2 stored as the pre-log 220A.

  If the snapshot storage condition is satisfied in step S12 (Yes in step S12), the management information including at least the nonvolatile table in the temporary storage area 111 of the DRAM 11 is used as the snapshot 210, and the management information of the NAND memory 12 is used. Save in the save area 126 (step S18). Then, it is determined whether or not there is an end instruction for the memory system 10 (step S19). If there is no end instruction, the process returns to step S12. If there is an end instruction, the process ends.

  Next, the management information restoring process of the memory system 10 by the management information restoring unit 155 will be described. FIG. 14 is a flowchart showing an example of a procedure for restoring the management information of the memory system, and FIG. 15 is a diagram for explaining the restoration process of the memory system. It is assumed here that the memory system 10 is connected to the host device and operates as a secondary storage device of the host device.

  First, when the host device is turned on by recovery from an instantaneous interruption or the like and a startup instruction is issued to the memory system 10 (step S31), the management information restoration unit 155 stores the management information storage area 126 in the NAND memory 12. The root pointer 240 and the second pointer 230 are sequentially read (step S32), and the addresses of the respective blocks storing the snapshot 210 and the preceding and following logs (previous log 220A, subsequent log 220B) are acquired (step S33). The snapshot 210 is acquired (step S34).

  Thereafter, the management information restoring unit 155 refers to the previous log 220A and the subsequent log 220B in the NAND memory 12 to determine whether or not an instantaneous interruption has occurred (step S35). For example, if the pre-log 220A and the post-log 220B exist in the NAND memory 12, it is determined that an instantaneous interruption has occurred. The determination as to whether or not an instantaneous interruption has occurred may be made by comparing the previous log 220A and the subsequent log 220B, for example. In the present embodiment, the front log 220A and the back log 220B store the same information. For this reason, for example, if the number of pages stored as the previous log 220A and the number of pages stored as the subsequent log 220B do not match, it can be determined that an instantaneous interruption has occurred. Further, the presence or absence of an instantaneous interruption may be determined based on the presence or absence of an ECC error, the data of the page stored as the previous log 220A, or the data of the page stored as the subsequent log 220B.

  When a momentary interruption occurs (Yes in step S35), the timing at which the momentary interruption occurs is confirmed based on the latest previous log 220A and latest latest log 220B in the NAND memory 12 (step S36).

  Furthermore, the management information restoration unit 155 determines whether or not the timing at which the instantaneous interruption occurred is in the process of storing the later log 220B (step S37). For example, when the last page in the later log 220B is in the middle of writing, the last page cannot be read, so it is determined that an instantaneous interruption has occurred during the saving of the later log 220B. Further, when the last page in the previous log 220A is being written, the last page cannot be read, so it is determined that an instantaneous interruption has occurred during the storage of the previous log 220A. In addition, when the log is written in the last page in the previous log 220A and the log is not written in the last page in the rear log 220B, an instantaneous interruption occurred during the data writing. It is judged.

  The management information restoration unit 155 selects the latest previous log 220A when it is determined that the timing at which the instantaneous interruption occurs is that the later log 220B is being saved (Yes in step S37) (step S38). On the other hand, if the management information restoration unit 155 determines that the timing at which the instantaneous interruption occurred is not being stored in the post-log 220B (No in step S37), the management information restoration unit 155 displays the latest post-log 220B that has been saved. Select (step S39). In other words, when the last page in the previous log 220A is in the middle of writing, the log is written in the last page in the previous log 220A, and the log is written in the last page in the rear log 220B. If not, the latest post-log 220B is selected.

  Thereafter, the selected log (previous log 220A or post log 220B) is acquired from the log storage block and expanded in the work area 112 of the DRAM 11 (step S40). Then, the management information (non-volatile table) is restored to the snapshot 210 in order from the oldest log (step S41), and the management information restoration process ends.

  On the other hand, if no instantaneous interruption has occurred (No in step S35), the management information is restored in the management information storage area 111 of the DRAM 11, and the management information restoration process is terminated.

  Note that the management information restoration unit 155 determines whether the number of pages stored as the previous log 220A and the number of pages stored as the subsequent log 220B regardless of whether or not the log is destroyed due to instantaneous interruption. Based on this, the management information may be restored by selecting either the previous log 220A or the subsequent log 220B. For example, when the number of pages stored as the previous log 220A is the same as the number of pages stored as the subsequent log 220B, the management information restoring unit 155 selects the previous log 220A and restores the management information. . The management information restoration unit 155 restores the management information by selecting the subsequent log 220B when the number of pages stored as the previous log 220A is larger than the number of pages stored as the subsequent log 220B. To do.

  FIG. 15 is a diagram illustrating an example of a configuration of a log storage area that stores the previous log 220A or the subsequent log 220B. FIG. 15 shows the second pointer 230 and the log 220 that is either the previous log 220A or the subsequent log 220B in the configuration shown in FIG. 8, and the other is omitted.

  The log 220 is composed of log information stored in each page indicated by diagonal lines in a log storage area constituted by log storage blocks 45 and 46, for example. Here, the number of log storage blocks constituting the log storage area is determined according to the size (log length) of the saved log. In other words, in the log storage area, log storage blocks are allocated sequentially according to the size of the log to be saved, and when logs are written to all pages of the log storage block being written, the next allocated log Logs are written to the storage block. In the illustrated example, the log is stored in order from the first page of the log storage block 45, and after the log is written to all the pages in the log storage block 45, the log storage block secured as the next writing block is used. A state in which logs are stored in order from the first page of the block 46 is shown.

  The second pointer 230 indicates the head address of the block indicating the storage position of the log 220, and specifically indicates the head page of the log storage block 45.

  The log storage block 45 has a pointer indicating the position of the log storage block 46. Specifically, when the first page of the log storage block 45 is used, the log storage block 46 is secured, and the first page of the log storage block 45 indicates the address of the first page of the log storage block 46. Pointer information is added. Accordingly, the second pointer 230, the log storage block 45, and the log storage block 46 can be traced in order, and the latest log for the snapshot 210 can be reached. Although not shown, the log storage block 46 has a pointer indicating the position of the next reserved log storage block. That is, when the first page of the log storage block 46 is used, a next log storage block (not shown) is secured, and the first page of the log storage block 46 has a head of the next log storage block. Pointer information indicating the page address is added. In FIG. 15, as an example, a case where logs are stored in two log storage blocks (log storage blocks 45 and 46) has been described, but logs are stored in three or more log storage blocks. The same applies to the case.

  As described above, in this embodiment, when the log storage area is configured by a plurality of log storage blocks, pointer information indicating the position of the next log storage block to be secured on the first page of the log storage block. And the log saved in the different log storage block is traced via the pointer. In other words, the log storage area is composed of sequentially reserved log storage blocks, and a structure in which log storage blocks are connected in a chain via pointers pointing between the log storage blocks (hereinafter referred to as log chains). ).

  According to this embodiment, even when the size of the log 220 stored in the log storage area (that is, the previous log 220A or the subsequent log 220B) exceeds the size of the log storage block, a new log storage block is created. Since the log can be secured and written, it is not necessary to save the snapshot 210 and update the second pointer 230 each time the log storage block becomes full. This reduces writing to the second pointer storage block in which the second pointer 230 is stored. Therefore, it is possible to reduce the number of times of writing to the NAND memory 12 and to suppress the shortening of the lifetime.

  Note that the timing at which the log storage block secures the pointer is not limited to using the first page, and may be when using another page. Therefore, for example, the log storage block 45 secures the log storage block 46 at the time when writing of the log is finished on the last page, and provides a pointer indicating the address of the first page of the log storage block 46. Also good.

  It is preferable to set an upper limit on the number of log storage blocks that can be secured in the log storage area. This is because if the size of the log 220 exceeds a predetermined size, the restoration time becomes longer when it is necessary to restore the management information by reflecting the log 220 in the snapshot 210. As described above, when the log storage area is filled, the snapshot saving condition (2) is satisfied, and a new snapshot 210 is acquired.

  In this embodiment, the front log 220A and the rear log 220B are acquired and the log is duplicated. However, even when one of the logs is acquired and the logs are not multiplexed, the above log chain is used. The same effect can be obtained by applying the configuration.

  FIG. 16 is a diagram showing an example of the configuration of the previous log storage area for storing the previous log 220A and the subsequent log storage area for storing the subsequent log 220B. As in FIG. 15, among the configurations shown in FIG. The second pointer 230, the previous log 220A and the rear log 220B are shown, and the others are omitted.

  As shown in FIG. 16, the pre-log storage area for storing the pre-log 220A and the post-log storage area for storing the post-log 220B are shown in FIG. 15, except for pointers provided between each other as described below. The log storage area has the same configuration. That is, the previous log storage area for storing the previous log 220A is composed of, for example, two log storage blocks 50 and 51, which are log storage blocks, and the log storage block 50 follows the log storage block 50. And a pointer indicating the position of the log storage block 51 secured in this way (in the figure, an arrow pointing from the first page of the log storage block 50 to the first page of the log storage block 51). The post-log storage area for storing the post-log 220B includes, for example, two log storage blocks 60 and 61 that are log storage blocks, and the log storage block 60 follows the log storage block 60. And a pointer (in the figure, an arrow pointing from the first page of the log storage block 60 to the first page of the log storage block 61). Further, the second pointer 230 indicates the first page of the log storage block 50 in the previous log storage area and the first page of the log storage block 60 in the subsequent log storage area.

  In FIG. 16, in addition to the log chain structure provided in each of the preceding log storage area and the subsequent log storage area, the log storage block 50 in the previous log storage area is used for log storage in the subsequent log storage area. It has a pointer indicating the position of the block 61 (in the figure, an arrow pointing from the first page of the log storage block 50 to the first page of the log storage block 61), and the log storage block 60 in the subsequent log storage area It has a pointer (an arrow pointing from the first page of the log storage block 60 to the first page of the log storage block 51) indicating the position of the log storage block 51 in the log storage area.

  That is, the log storage block 50 in the previous log storage area includes the log storage block 51 in addition to the pointer indicating the position of the log storage block 51 which is the next log storage block secured in the previous log storage area. Log storage blocks secured in the subsequent log storage area in the same order (in this case, the log storage block 51 is secured second, in this case), that is, the log storage block 61 It has a pointer that indicates the position. Similarly, the log storage block 60 in the post-log storage area includes the log storage block 60 in addition to the pointer indicating the position of the log storage block 61 which is the next log storage block secured in the post-log storage area. Log storage block secured in the previous log storage area in the same order as the block 61 securement order (in this case, the log storage block 61 is secured second, so the log storage block) A pointer indicating the position 51 is provided.

  As described above, since the previous log 220A and the rear log 220B store the same log information, the front log 220A and the rear log 220B have the same log information unless an abnormality such as a momentary interruption occurs. Is saved. Therefore, the log stored in each page of the log storage block 50 is the same as the log stored in the corresponding page of the log storage block 60 and is stored in each page of the log storage block 51. The log stored in the log storage block 61 is the same as the log stored in the corresponding page. Therefore, the log storage block 50 in the previous log storage area has a pointer indicating the position of the log storage block 61 in the subsequent log storage area in addition to the pointer indicating the position of the log storage block 51, thereby The location of the log storage block 61 that stores the same log information as the block 51 is secured as a backup. Similarly, the log storage block 60 in the subsequent log storage area has a pointer indicating the position of the log storage block 51 in the previous log storage area in addition to the pointer indicating the position of the log storage block 61, thereby The location of the log storage block 51 that stores the same log information as the storage block 61 is secured as a backup. Although not shown, the log storage block 51 has a pointer indicating the position of the log storage block secured next to the log storage block 51 in the previous log storage area, and the subsequent log storage area. 2 has a pointer indicating the position of the log storage block secured next to the log storage block 61. Similarly, although not shown, the log storage block 61 has a pointer indicating the position of the log storage block secured next to the log storage block 61 in the subsequent log storage area, and the previous log storage area. 2 has a pointer indicating the position of the log storage block secured next to the log storage block 51. In FIG. 16, as an example, logs are stored in two log storage blocks (log storage blocks 50 and 51 and log storage blocks 60 and 61) in the previous log storage area and the subsequent log storage area, respectively. However, the same applies to the case where logs are stored in three or more log storage blocks.

  In this way, by duplicating the pointers of each log storage block in the previous log storage area and the subsequent log storage area, it is possible to easily restore the log even when the log is destroyed due to an instantaneous interruption or the like. Can do. For example, when an instantaneous interruption occurs during writing of the log storage block 51 and the log data of the page being written and its lower page are destroyed, a pointer to the log storage block 61 of the log storage block 50 is set. Since the log can be obtained from the log storage block 61 by using the log, the log of the log storage block 51 can be easily restored. As described above, by duplicating the pointer, it is possible to prevent the log information from being lost regardless of the timing when the instantaneous interruption occurs. By using either one, it is possible to easily return the memory system 10 to the state before the instantaneous interruption occurs.

  In the above, the second pointer 230 is provided as a pointer indicating the storage position of the snapshot 210, the previous log 220A, and the subsequent log 220B, and the root pointer 240 is provided as a pointer indicating the storage position of the second pointer 230. Although the pointer has two stages, for example, the pointer may have one stage.

  Further, the head pointers of the front log 220A and the back log 220B may be stored in the snapshot 210 instead of in the second pointer storage block.

  The data management unit in the DRAM 11 is a page size unit, the data write / read unit in the NAND memory 12 is a page size unit, and the erase unit and the management unit are block size units. However, the present invention is not limited to this. It is possible to use arbitrary units for each purpose.

  Further, although the case where a DRAM is used as the first storage unit is illustrated, another volatile semiconductor storage device or a nonvolatile semiconductor storage device may be used.

  The charge storage layer is not limited to the floating gate type, and may be a charge trap type using a silicon nitride film such as a MONOS (Metal-Oxide-Nitride-Oxide-Semiconductor) structure or other methods.

It is a block diagram which shows an example of a structure of the memory system concerning embodiment of this invention. It is a circuit diagram which shows an example of a structure of one block contained in NAND memory. It is a figure which shows typically the function structure of DRAM and NAND memory. It is a figure which shows an example of the layer structure which manages the data memorize | stored in a memory system. It is a figure which shows an example of cache management information. It is a figure which shows an example of logical NAND management information. It is a figure which shows an example of NAND intrinsic | native substance conversion information. It is a figure which shows typically an example of the content of the management information storage information memorize | stored in a management information storage area. It is a figure which shows an example of a log. It is a block diagram which shows an example of a function structure of a drive control part. It is a block diagram which shows an example of a function structure of the data management part concerning embodiment. It is a flowchart which shows an example of the preservation | save processing procedure of the management information of a memory system. It is a figure for demonstrating the preservation | save process of a front log and a back log. It is a flowchart which shows an example of the restoration process procedure of the management information of a memory system. It is a figure which shows an example of a structure of a log storage area. It is a figure which shows an example of a structure of the front log storage area which stores the front log 220A, and the back log storage area which stores the back log 220B.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Memory system, 11 ... DRAM, 12 ... NAND memory, 13 ... Power supply circuit, 14 ... Drive control part, 15 ... Bus, 31 ... DRAM management layer, 32 ... Logical NAND management layer, 33 ... Physical NAND management layer, 41 ... cache management information, 42 ... management information, 42a ... logical page management information, 42b ... logical block management information, 43 ... NAND internal / physical conversion information, 45, 46, 50, 51, 60, 61 ... log storage blocks, DESCRIPTION OF SYMBOLS 111 ... Temporary storage area, 112 ... Work area, 125 ... Data storage area, 126 ... Management information storage area, 141 ... Data management part, 151 ... Data transfer processing part, 152 ... Management information management part, 153 ... Write management information 154... Management information storage unit 155... Management information restoration unit 156... Log storage block release unit 210. ... log, 220A ... before the log, 220B ... post-log, 230 ... second pointer, 240 ... root pointer

Claims (4)

A volatile first storage unit;
A non-volatile second storage unit composed of memory cells capable of storing multi-value data;
Management information including the storage location of the data stored in the second storage unit at the time of activation is transferred between the host device and the second storage unit via the first storage unit. A controller that takes in the first storage unit and performs data management in the first and second storage units based on the management information while updating the management information taken in;
With
The second storage unit is acquired when a predetermined condition is satisfied, and a snapshot storage area that stores the snapshot that is the management information of the first storage unit and the management information are changed. A log storage area that stores a log that is difference information before and after the change, and a pointer storage area that stores a first pointer indicating a storage position of the snapshot storage area and the log storage area ,
The log storage area is configured by sequentially securing blocks that are data erasure units according to the size of the log to be stored,
The block has a second pointer indicating the position of the next reserved block. The log storage area is a pre-update log storage area for storing a pre-update log, which is a log saved before the management information is updated, and a log having the same content as the pre-update log and the management information A post-update log storage area for storing a post-update log that is a log saved after the
Each of the pre-update log storage area and the post-update log storage area is configured by sequentially securing the same number of blocks as data erasure units according to the size of the pre-update log or the post-update log to be stored,
In addition to the second pointer indicating the position of the next block secured in the pre-update log storage area, the block in the pre-update log storage area includes the next block secured in the pre-update log storage area. A third pointer indicating the position of the block secured in the updated log storage area in the same order as the secured order;
In addition to the second pointer indicating the position of the next block secured in the post-update log storage area, the block in the post-update log storage area is the block of the block secured next in the post-update log storage area. 2. The memory system according to claim 1, further comprising a fourth pointer indicating a position of a block secured in the pre-update log storage area in the same order as the securing order. A volatile first storage unit;
A non-volatile second storage unit composed of memory cells capable of storing multi-value data;
Management information including the storage location of the data stored in the second storage unit at the time of activation is transferred between the host device and the second storage unit via the first storage unit. A controller that takes in the first storage unit and performs data management in the first and second storage units based on the management information while updating the management information taken in;
With
The second storage unit is acquired when a predetermined condition is satisfied, and a snapshot storage area that stores the snapshot that is the management information of the first storage unit and the management information are changed. A log storage area that stores a log that is difference information before and after the change, and a pointer storage area that stores a first pointer indicating a storage position of the snapshot storage area,
The log storage area is configured by sequentially securing blocks that are data erasure units according to the size of the log to be stored,
A second pointer indicating the storage position of the first log stored in the log storage area is stored in the snapshot,
The block has a third pointer indicating the position of the next reserved block. A volatile first storage unit;
A non-volatile second storage unit composed of memory cells capable of storing multi-value data;
Management information including the storage location of the data stored in the second storage unit at the time of activation is transferred between the host device and the second storage unit via the first storage unit. A controller that takes in the first storage unit and performs data management in the first and second storage units based on the management information while updating the management information taken in;
With
The second storage unit stores a log storage area for storing a log that is difference information before and after the change when the management information is changed, and a snapshot that is the management information of the first storage unit. A snapshot storage area to store,
The controller acquires the snapshot when the log storage area is filled with a log and when the log storage area becomes a defective area where data cannot be stored, and stores the snapshot in the snapshot storage area. A featured memory system.

Images