Re: Mild filesystem corruption on ext4 (no journal)

From: Alan Jenkins
Date: Fri Jun 05 2009 - 17:31:33 EST


Eric Sandeen wrote:
Alan Jenkins wrote:
Eric Sandeen wrote:

Maybe you could try some things in your shutdown script, such as
explicitly fsyncing the file, or bmapping it with filefrag, or dropping
caches and rereading it... see what the state is just before the
shutdown compared to after the reboot.

-Eric
Dropping caches (and running sync first) had no effect on the result of md5sum. Hopefully that narrows it down a bit.

And did the reread after dropping caches have the right data?

Yes.

Did the block numbers reported by filefrag -v change post-boot?

Oh, I didn't understand that's what you were asking for.

The bug report Ted linked to says it's (most likely) a writeback issue. In which case I think the block numbers won't change. I'll check tomorrow, and follow-up if it turns up any unexpected result.

There's also speculation that it's a core kernel issue, something that changed since 2.6.26. Perhaps that explains how remount-ro + sync + drop_caches can leave the correct data sitting in the pagecache, without either writing it to disk or dropping it.

Thanks
Alan
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