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Re: How well ext3 will tolerate errors?


On Sat, Apr 20, 2002 at 03:31:16PM +0300, Jani Averbach wrote:
> I would like to know how well ext3/(ext2) will tolerate underlaying
> errors (I am planning to use loop-AES backed ext3 fs).
> So if there is 1024 bytes corruption of data what will be the worst case:

Define corruption.  Do you mean lost data, or bogus data?

> - If this data belongs to some file, this part of data(file) has been
>   lost?

If you get "corruption" as opposed to unrecoverable data, then the
file contents are not just lost, they are garbled silently.  In other
words, the application will get bogus data back, rather than being
told there was a problem via an EIO error.

> - If this data belongs to superblock, I have to repair ext3 and use
>   another superblock?


> - If this data belongs to journaling system, I have to ??? or ??? will
>   happen?

The journal area is mostly unused unless you crash.  If that happens,
e2fsck needs to take care of things.  If the error is EIO, the worst
that can happen right now is that e2fsck will complain, and you'll
have to manually remove the journal (with tune2fs) then re-run e2fsck.
If the error is data corruption, then either parts of the journal will
be silently ignored (corrupting active metadata on the fs), or you'll
end up copying garbage to active filesystem metadata.

> Is above right? Is there any other case that I don't find?

Bitmaps, inode tables, directories.


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