JPH11282765A - External storage device using flash memory - Google Patents

Abstract

(57) [Summary] [Problem] Because flash memory has a long writing time,
If data is written to an external storage device using a flash memory at the time of a power failure, data and management information become unstable, and data stored in the external storage device may be destroyed. A flash memory used as a storage medium, a host interface, a control circuit for controlling the flash memory, a host interface bus between the host interface and the control circuit, a host interface control line, a flash memory and a control circuit , A memory address bus, a memory data bus, and a memory control line.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of preventing data destruction at the time of a power failure during data writing to an external storage device of a computer using a flash memory as a nonvolatile memory.

[0002]

2. Description of the Related Art As an external storage device, there is a magnetic disk drive (hard disk drive, hereinafter referred to as H / D). H / D has a large capacity, but has drawbacks that it is susceptible to shock and vibration because it uses mechanical parts. To solve this drawback, an external storage device using a flash memory as a storage medium has been developed.

An external storage device performs read and write access in sector units. The size of the sector is 512
Bytes are often used.

A flash memory has a structure of its element,
Erasing must be performed before writing. The read access time is fast, but the erase time and the write time are long. Furthermore, the flash memory currently has a
There is a limit of 0 ⁵ times. When a certain portion in the flash memory reaches the limit of the number of times of writing due to concentration of writing, even if other areas of the flash memory can be used, they cannot be used as an external storage device.

For this reason, conventionally, the flash memory is divided into physical sectors for storing data of a sector size, and write data from the host is written in a ring buffer format from a physical sector having a small address to a physical sector having a large address in the flash memory. Some write-once data writing methods were used. This write-once type data writing method reduces the erasing wait time before writing and avoids the concentration of writing to a certain part of the flash memory, thereby extending the life of the flash memory and reducing external storage using the flash memory. It is possible to extend the life of the device.

[0006]

In the conventional method, the physical sector in the flash memory is divided into a data area for holding write data from the host and a management area, and the management area has a logical sector which is an access address of the host. An invalidation flag indicating the validity of the data written in the address and the data area is provided.

When writing data from the host, the write data from the host is written to the data area of the physical sector of the flash memory, and then the logical sector address, which is the access address of the host, is written to the management area of the physical sector. The physical sector storing the write data from the host is updated to the address of the next physical sector.

An external storage device using a flash memory has a control circuit. The control circuit has a mapping table for converting a logical sector address, which is an access address from the host, into a physical sector address in the flash memory. It has a pointer indicating the address of the physical center that stores the next write data. The mapping table and pointer are updated on every write from the host, and are therefore created on the RAM.

When the power of the external storage device is turned off, the contents of the RAM are erased. Therefore, when the power of the external storage device is turned on, the control circuit accesses the management area of each physical sector of the flash memory and creates a mapping table and a pointer. The pointer uses the initial value after erasure (normal bit value is 1) for the portion where writing to the flash memory is not performed, and uses the physical sector in which the logical sector address of the management area takes the initial value of the flash memory for the first time. Address.

[0010] However, if a power failure occurs during writing to the flash memory, the data at the writing location is undefined. If a power failure occurs during writing to the data area of the physical sector, the data in the data area of the physical sector becomes undefined.
In the conventional method, the value of the pointer created at the time of power recovery is the address of the physical sector that was being written during the power failure, and the data area was written by the host even though indefinite data was written. Because the data is written,
Normal data cannot be written.

If a power failure occurs during the writing of the logical sector address in the management area, the logical sector address being written becomes undefined. Assuming that this value is x, if x is a logical sector address that actually exists, the value of the physical sector address for the logical sector address x in the mapping table created at the time of power restoration will be different from the actual value, Different data is read from the data.

As described above, the conventional method has a problem that data in an external storage device is destroyed when a power failure occurs during writing to a flash memory.

According to the present invention, the life of the flash memory is extended by reducing the erasing wait time before writing and avoiding the concentration of writing at a certain location in the flash memory, and the life of the external storage device using the flash memory. While avoiding destruction of stored data due to a power failure during writing to an external storage device using a flash memory, and ensuring the validity of the stored data.

[0014]

An object of the present invention is to provide a host interface, a flash memory used as a storage medium, a host interface, a control circuit for controlling the flash memory, a host interface bus between the host interface and the control circuit, It comprises a host interface control line, a memory address bus between the flash memory and the control circuit, a memory data bus, and a memory control line.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration example of the present invention. An external storage device 100 using the flash memory according to the present invention is connected to the host 200. 1 is a host interface. Reference numeral 2 denotes a flash memory used as a storage medium of the present invention. A control circuit 3 controls the host interface 1 and the flash memory 2. The control circuit 3 controls the host interface 1 via the host interface bus 4 and the host interface control line 5. The flash memory 2 is controlled by a control circuit 3 via a memory address bus 6, a memory data bus 7, and a memory control line 8.

FIG. 2 shows the configuration of the flash memory 2.
The inside of the flash memory 2 is divided into physical sectors 20, which are data read / write units. 512 bytes are often used as the size of the sector data.

FIG. 3 shows the configuration of the physical sector 20. The physical sector 20 includes a data area 21 for storing write data from the host 200 and a management area 22 for storing management information of the physical sector.

FIG. 4 shows the management area 22 in the conventional system.
It is a structure of. It is composed of a logical sector address 23, which is an access address of the host 200 for data written in the data area 21, and an invalid flag 24 indicating the validity of the data written in the data area 21.

FIG. 5 shows the configuration of the management area 22 in the method proposed this time. In addition to the logical sector address 23 and the invalid flag 24, a write start flag 25 indicating the start of writing in the data area 21, a write indicating that writing of data to the data area 21 and writing of the logical sector address 23 of the management area 22 have been completed. It consists of an end flag 26.

FIG. 6 shows a state in which the host 200 sends the external storage device 1.
Flash memory 2 when data was written to 00
The method of writing data to the memory will be described. Due to the structure of the flash memory, erasing must be performed before writing. The read access time is fast, but the erase time and the write time are long. In addition, flash memory is at present there is a limit of 10 ⁵ times the number of writes. When a certain portion in the flash memory reaches the limit of the number of times of writing due to concentration of writing, even if other areas of the flash memory can be used, they cannot be used as an external storage device.

Therefore, as shown in FIG. 6, a write-once data write method in which write data from the host 200 is written in the ring buffer format from the physical sector 20 having a small address to the physical sector 20 having a large address in the flash memory 2. I take the. In FIG. 6, it is assumed that the host 200 has written N-1 times to the external storage device 100. The shaded physical sector 20 represents a written physical sector, and write data from the host 200 is stored in the shaded physical sector 20.

In the write-once type data writing method, the head of an empty physical sector to which data has not been written is a physical sector for storing write data from the next host 200. In FIG. 6, the physical sector 20 in which the N-th (next) write is written is a physical sector in which the next write data from the host 200 is stored. In FIG. 6, if writing is performed on the physical sector written as N-th (next) writing, then the host 2
The write data starting from 00 is stored in the physical sector written as the Nth (next) write.

This write-once type data writing method reduces the erasing wait time before writing and avoids the concentration of writing at a certain location in the flash memory 2, thereby extending the life of the flash memory 2. It is possible to prolong the life of the external storage device 100 using the.

In the external storage device 100, a mapping table for converting a logical sector address into a physical sector address in the flash memory and a pointer indicating the address of the physical sector for storing the next write data from the host are stored in the control circuit 3. Have.

FIG. 7 is a diagram showing the external storage device 1 from the host 200.
This represents a change in the state of the flash memory 2 when data of the logical sector address A is written to 00. The upper part of FIG. 7 stores write data from the host 200 in the flash memory 2.
Shows that writing is in progress. The old data of the logical host address A is stored in the first physical sector.
Since the writing of data from 00 has not been completed, it is treated as valid data. Since the shaded portion is a written physical sector, the physical address A new data write is written. The address of the leading physical sector of the empty physical sector is used as a pointer.

The lower part of FIG. 7 shows a state after the writing of the write data from the host 300 to the flash memory 2 is completed. The physical sector in which the writing of the logical address A new data has been written is shaded because the writing of data from the host 200 has been completed. Then, the first physical sector storing the old data of the logical sector address A is invalidated.

The physical sector address corresponding to the logical sector address A in the mapping table is changed from the first physical sector address in FIG. 7 to the address of the physical sector in which the writing of the logical address A new data is completed. The pointer is changed from the address of the physical sector in which the writing of the logical address A new data is completed to the address of the next physical sector.

FIGS. 8 to 10 show a conventional method of FIG.
The details of the operation will be described. The upper physical sector in FIGS. 8 to 10 represents the first physical sector in FIG. 7, and the lower physical sector in FIG. 8 to FIG. Indicates the center. The initial value of the data after the execution of the erasure of the flash memory 2 is 1 as a bit value.

FIG. 8 shows execution of writing of write data from the host 200 to the data area 21 of the lower physical sector 20. In the upper physical sector 20 storing the old data of the logical sector address A, the data area 21
And the logical sector address 23 has been written.

FIG. 9 shows that the A is written to the logical sector address 23 because the writing of the data area 21 of the lower physical sector 20 has been completed in the next operation of FIG.

FIG. 10 shows the next operation of FIG. 9 because the writing of new write data from the host 200 and the writing of the logical sector address A to the lower physical sector 20 have been completed.
The invalid flag of the upper physical sector 20 storing the old data is rewritten from 1 which is the initial value of the flash memory to 0, and the data stored in the upper physical sector 20 is invalidated.

The invalidation of data stored in the physical sector 20 is performed in preparation for erasure when an erase block, which is an erase unit of the flash memory 2, is larger than the size of the physical sector 20. When erasing an erase block for the next write, the invalid flag 26 of each physical sector 20 in the erase block to be erased is checked, and if there is a physical sector containing valid data, it is moved to an empty physical sector. And then erase the erase block.

FIGS. 11 to 15 show details of the operation of FIG. 7 in the method proposed this time. Compared to FIGS. 8 to 10, 0 is written in the write start flag 25 before writing in the data area 21, and the write end flag 26 is written in the write end flag 26 after writing the logical sector address 23.
Is rewritten from the write initial value 1 to 0.
FIG. 11 shows the writing of 0 to the writing start flag 25, and FIG. 14 shows the writing of 0 to the writing end flag 26. 12 is shown in FIG. 8, FIG. 13 is shown in FIG.
Corresponds to FIG.

The mapping table and the pointer are stored in the host 2
Since it is updated every time data is written from 00, the control circuit 3
Is created on the RAM. When the power of the external storage device 100 is turned off, the contents of the RAM are erased. Therefore, when the power of the external storage device 100 is turned on, the control circuit 3 accesses the management area 22 of each physical sector 20 of the flash memory 2 and creates a mapping table and a pointer. I do.

In the conventional method, since the management area 22 contains only the logical sector address 23 and the invalidation flag 24, the mapping table stores the logical sector address 2
3 is not an initial value, but takes a range of a logical sector address that actually exists, and is created by creating a correspondence table between the logical sector address 23 and the logical sector address of the physical sector in which the invalidation flag 24 is not 0.

When there are a plurality of physical sectors 20 having the same value of the logical sector address 23, since the write-once type is being written to the flash memory 2, the last written physical sector 20 is determined. The address of the physical sector is registered in the mapping table. The pointer uses the fact that the logical sector address 23 has an initial value of 1 as a bit value for the portion where the physical sector 20 is not written, and uses the logical sector address 2 of the management area 22 as the pointer.
3 is the address of the physical sector 20 that takes the initial value for the first time.

When data is managed in the flash memory 2 of the external storage device 100 by the above-described method, if a power failure occurs or power is cut off while writing to the flash memory 2 is not performed, the external storage device 100 There is no corruption of the data stored within. However, physical sector 20
If a power failure occurs during writing to the external storage device 100, data stored in the external storage device 100 will be destroyed.

Referring to FIG. 16 and FIG.
External storage device 10 due to a power failure while writing to
The destruction of data stored in 0 will be described. The destruction of data is caused by the fact that if a power failure occurs during writing to the flash memory 2, the data at the write location is undefined.

FIG. 16 shows a physical sector 20 in which a power failure occurred during writing in the data area 21. Since a power failure occurred during writing in the data area 21, the value of the data in the data area 21 is undefined. When a pointer is created after power recovery by the conventional method, the logical sector address 23 of the physical sector 20 shown in FIG. 16 remains at the initial value, so that the physical sector 20 shown in FIG. This is a physical sector for storing data. However, in the physical sector 20 shown in FIG. 16, since undefined data has already been written in the data area 21, the next write data from the host 200 cannot be newly written normally.

The lower physical sector 20 in FIG. 17 represents the physical sector 20 in which a power failure occurred during the writing of the logical sector address 23. Since a power failure occurred during writing to the logical sector address 23, the logical sector address 23 is undefined.
Logical sector address 2 of lower physical sector 20 in FIG.
Assuming that the value of 3 is x, if x is a logical sector address that actually exists, there can be a physical sector 20 storing valid data at the logical sector address x as in the upper physical sector 20 in FIG. There is.

When the mapping table is created by the conventional method, the data storing the logical sector address x is registered as the lower physical sector 20 in FIG. As a result, the host 200 sends the logical sector address x
17 is read, the true value is the data written in the data area 21 of the upper physical sector 20 in FIG.
The data written in the data area 21 is read.

In the proposed method, the value of the write end flag 26 of the management area 22 of each physical sector 20 is 0 indicating that the writing of the logical sector address 23 has been completed. It is created by making a correspondence table with. Since only the physical sector for which the writing of the logical sector address 23 has been completed is subjected to the mapping table creation, the destruction of data as shown in FIG. 17 is eliminated.

In the proposed method, the mapping table does not refer to the logical sector address 23 of the management area 22 of each sector 20, but sets the address of the physical sector in which the value of the write start flag 25 becomes 1 for the first time. Since writing to the physical sector 20 is performed after setting the write start flag 25 to 0, as shown in FIG. 16, data such as writing write data from the host 200 to the data area 21 to which indefinite data is written is written. Destruction is gone.

[0044]

As described above, according to the present invention, the life of a flash memory can be extended by reducing the erasing wait time before writing and avoiding the concentration of writing at a certain location in the flash memory. It is possible to extend the life of the external storage device using the flash memory, avoid destruction of the stored data due to a power failure during writing to the external storage device using the flash memory, and guarantee the validity of the stored data. Become.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a configuration of an external storage device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a flash memory of FIG. 1;

FIG. 3 is a diagram showing a configuration of a physical sector in FIG. 2;

FIG. 4 is a diagram showing a configuration of a management area in a conventional method.

FIG. 5 is a diagram showing a configuration of a management area in a scheme proposed in the present invention.

FIG. 6 is a diagram illustrating a method of writing data to a flash memory when data is written from a host to an external storage device according to the present invention.

7 is a diagram showing a change in the state of the flash memory when data of a logical sector address A is written from the host of FIG. 6 to the external storage device.

FIG. 8 is a diagram showing details of a change in the state of the flash memory when data of a logical sector address A is written from a host to an external storage device in a conventional method.

FIG. 9 is a diagram showing details of a change in the state of the flash memory when data of a logical sector address A is written from a host to an external storage device in a conventional method.

FIG. 10 is a diagram showing details of a change in the state of a flash memory when data of a logical sector address A is written from a host to an external storage device in a conventional method.

FIG. 11 is a diagram showing details of a change in the state of the flash memory when data of the logical sector address A is written from the host to the external storage device in the method proposed in the present invention.

FIG. 12 is a diagram showing details of changes in the state of the flash memory when data of a logical sector address A is written from the host to the external storage device in the method proposed in the present invention.

FIG. 13 is a diagram showing details of a change in the state of the flash memory when data of the logical sector address A is written from the host to the external storage device in the method proposed in the present invention.

FIG. 14 is a diagram showing details of a change in the state of the flash memory when data of the logical sector address A is written from the host to the external storage device in the method proposed in the present invention.

FIG. 15 is a diagram showing details of a change in the state of the flash memory when data of the logical sector address A is written from the host to the external storage device in the method proposed in the present invention.

FIG. 16 is a diagram illustrating a physical sector in which a power failure occurs during writing of a data area according to the present invention.

FIG. 17 is a diagram illustrating a physical sector in which a power failure occurs during writing of a logical sector address according to the present invention.

[Explanation of symbols]

1. Host interface, 2. Flash memory, 3.
... Control circuit, 4 ... Host interface bus, 5 ... Host interface control line, 6 ... Memory address bus, 7
... memory data bus, 8 ... memory control line, 20 ... physical sector, 21 ... data area, 22 ... management area, 23 ... logical sector address, 24 ... invalid flag, 25 ... write start flag, 26 ... write end flag, 100 ... external storage device, 200 ... host.

Claims (2)

[Claims] A flash memory is used as a storage medium, and the inside of the flash memory is divided into physical sectors as data read / write units, and write data from a host is written in a ring buffer format from a physical sector having a small address to a large address of the flash memory. A write-once type data writing method of writing data to a physical sector is used. The physical sector is divided into a data area for holding write data from the host and a management area, and the management area has a logical sector address and data which are the access address of the host. In addition to the invalidation flag indicating the validity of the data written in the area, a write start flag indicating the start of writing in the data area, indicating that the writing of data to the data area and the writing of the logical sector address of the management area have been completed. A write end flag is provided, and each item in the flash memory is By referring to the value of the write start flag in the management area of the sector and knowing the position of the physical sector where the last write was performed, the position of the next physical sector to be written next is determined, and the value of the write end flag is referred to. Determining the validity of the last written data in order to avoid destruction of the stored data due to a power failure during writing to the flash memory and to guarantee the validity of the stored data. External storage device used. 2. An external storage device using a flash memory according to claim 1, wherein a plurality of flash memories are used.