Re: [patch] ext2/3: document conditions when reliable operation is possible

From: Florian Weimer
Date: Mon Aug 24 2009 - 07:22:46 EST

* Pavel Machek:

> +Linux block-backed filesystems can only work correctly when several
> +conditions are met in the block layer and below (disks, flash
> +cards). Some of them are obvious ("data on media should not change
> +randomly"), some are less so.

You should make clear that the file lists per-file-system rules and
that some file sytems can recover from some of the error conditions.

> +* don't damage the old data on a failed write (ATOMIC-WRITES)
> +
> + (Thrash may get written into sectors during powerfail. And
> + ext3 handles this surprisingly well at least in the
> + catastrophic case of garbage getting written into the inode
> + table, since the journal replay often will "repair" the
> + garbage that was written into the filesystem metadata blocks.

Isn't this by design? In other words, if the metadata doesn't survive
non-atomic writes, wouldn't it be an ext3 bug?

Florian Weimer <fweimer@xxxxxx>
BFK edv-consulting GmbH
Kriegsstraße 100 tel: +49-721-96201-1
D-76133 Karlsruhe fax: +49-721-96201-99
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