Three comments

Posted Jul 20, 2006 16:20 UTC (Thu) by renox (guest, #23785)
In reply to: Three comments by ncm
Parent article: Crash-only software: More than meets the eye

> journaling file systems, like journaling databases, are no generally safe against power drops

I think that it depends on the type of journaling: journaling metadata only doesn't protect your files which can be corrupted, but among other ext3fs has a journaling data+metadata, which has a quite high performance impact, but it should 'protect' as in the data is here or not here but it isn't half here (seen with ReiserFSv3: the passwd file appended with binary data, urgh).

Of course even journaling 'data+metadata' can work correctly only if the disk obey some order of writing the data.

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Three comments

Posted Jul 20, 2006 23:43 UTC (Thu) by ncm (guest, #165) [Link]

...even journaling 'data+metadata' can work correctly only if the disk obey some order of writing the data.

Precisely the point. However, data+metadata journaling may be kind of pointless if you don't have any way of telling how much of the data you had meant to have written was, in fact, written. For example, if you have an outage while compiling a kernel, no amount of journaling can make it safe to skip "make clean" before running "make" again. That makes the cheapest, fastest journaling regime also best, for such an environment.