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SubjectRe: ReiserFS data corruption in very simple configuration
foner-reiserfs@media.mit.edu writes:
> [Please CC me on any replies; I'm not on linux-kernel.]
>
> The ReiserFS that comes with both Mandrake 7.2 and 8.0 has
> demonstrated a serious data corruption problem, and I'd like
> to know (a) if anyone else has seen this, (b) how to avoid it,
> and (c) how to determine how badly I've been bitten.
>
> My configuration in each case has been an AMD CPU running ReiserFS
> exactly as configured "out of the box" by running the Mandrake 7.2 or
> 8.0 installation CD and opting to run ReiserFS instead of the default.
> This is a uniprocessor machine with one IDE 80GB Maxtor disk---no RAID
> or anything fancy like that. The hardware itself is rock solid and
> has never demonstrated any faults at all. (MDK 8.0 appears to use
> RSFS 3.6.25; I'm not longer running MDK 7.2, so I can't check that.)
> The machine had barely been used before each corruption problem; I'm
> not running some strange root-priv stuff, and each time, the FS hadn't
> had more than a few minutes to a few hours of use since being created.
>
> In each case, I've gotten in trouble by editing my XF86Config-4 file,
> guessing wrong on a modeline, hanging X (blank gray screen & no
> response to anything), and being forced to hit the reset button
> because nothing else worked. Under 7.2, I discovered that my
> XF86Config-4 file suddenly had a block of nulls in it. That time, I
> thought I must have been hallucinating, but I ran a background job to
> sync the filesystem every second while continuing to debug the X
> problems, and didn't see the corruption again.
>
> Now, I was just bitten by the -same- behavior under MDK 8.0. After
> accidentally hanging X, I waited a few seconds just in case a sync was
> pending, hit reset, and had all sorts of lossage:
> (1) Parts of the XF86Conf-4 file had lines garbled, e.g.,
> sections of the file had apparently been rearranged.
> (2) /var/log/XFree86.0.log was truncated, and maybe garbled.
> (2) Logging in as root was fine, but then logging in as myself
> I got "Last login: <4-5 lines of my XFree86.0.log file (!)>"
> instead of a date! Logging in again gave me the proper
> last-login time, but clearly wtmp or something else had
> gotten stepped on in some weird way.
> Obviously, the behavior I saw once under MDK 7.2 was no hallucination
> or accidental yank in Emacs.
>
> I thought the whole point of a journalling file system was to
> -prevent- corruption due to an unexpected failure! This seems to be
> -far- worse than a normal filesystem---ext2fs would at least choke and
> force fsck to be run, which might actually fix the problem, but this
> is ridiculous---it just silently trashes random files.

Stock reiserfs only provides meta-data journalling. It guarantees that
structure of you file-system will be correct after journal replay, not
content of a files. It will never "trash" file that wasn't accessed at
the moment of crash, though. Full data-journaling comes at cost. There
is patch by Chris Mason <Mason@Suse.COM> to support data journaling in
reiserfs. Ext3 supports it also.

>
> So I now have possibly-undetected filesystem damage. My -guess- is
> that only files written within a few minutes of the reset are likely
> to be affected, but I really don't know, and don't know of a good way
> to find out. Must I reinstall the OS -again-, starting from a blank
> partition, to be sure? Maybe I should just give up on ReiserFS completely.
>
> [If there is a more-appropriate place for me to send this---such as
> a particular Mandrake list, or a particular ReiserFS list---please let
> me know, particularly if I can get a quick answer -without- going

Reiserfs mail-list <Reiserfs-List@Namesys.COM>,
archive at http://marc.theaimsgroup.com/?l=reiserfs&r=1&w=2

> through the overhead of subscribing to the list, being flooded, and
> unsubscribing---that's what archives are for. Some websearching
> for "ReiserFS corruption" yielded -thousands- of hits---not a good
> sign---and a very large proportion of them were on this list, so I
> figure this is as good a place to ask as any. Thanks again.]

Nikita.
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