LVM negates benefits of jounaling filesystems? [was RFE: autofsck]

[Callum Lerwick]

On Tue, Jun 10, 2008 at 9:53 AM, Eric Sandeen <sandeen at redhat.com> wrote:

> I think the problem is, barriers are really implemented as drive cache
> flushes.  So under certain workloads the performance really does hurt.
> But if the alternative is a good chance of filesystem corruption on
> power loss, remind me again why we run a journaling fileystem at all?  :)
>
> If ext3 doesn't get barriers on by default upstream then I would suggest
> that yes, we should patch the kernel ourselves to do so, or set the
> installer to create fstabs which specify it for filesystems that don't
> have barriers on by default.  ... after lvm stops filtering it out, anyway.


I would like to put in my +1 for this. Performance is pointless on if you
can not trust that your data is safe. I have on many occasions run fscks on
my supposedly clean ext3 filesystems, only to find some mild corruption. How
can this happen? Isn't journaling supposed to prevent this? One day I ran a
fsck before doing some filesystem resizing, only to find one of my
irreplacible personal photos had become corrupted. I had no way to know when
or why this file got corrupted, it had been written to disk some time ago
and never touched since. I trusted journaling, and it failed me. (Yes, I
have a backup. I think...) After this, I now turn on autofsck on all my
machines, so that corruption at least can't go undetected for years. Which
means after a power fail it takes my primary desktop with a pretty full
250gb drive 20-30 minutes to come back up, which is incredibly irritating,
but I have to know my data is safe. I've even picked up a habit of
obsessively checksumming all my really important files. I wish the
filesystem would help do this for me. (ZFS...)

Knowing is half the battle. See, what can happen here, is a file can get
corrupted, and I may not notice until years later. By then I may have cycled
through several full backups, and long since lost the backup I did have of
the file...

This must be fixed. Only through a long painful process of losing faith have
I learned to not trust my filesystems. I suspect there are many others out
there who have been bitten by filesystem corruption and just don't know it
yet.

Only now do I learn the likely reason for this corruption. How would I have
reported this? I just assumed it was hardware glitches.
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