

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

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