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

[Ahmed Kamal]

Reference this: http://blogs.sun.com/bonwick/entry/casablanca
Does anyone know if we're getting ZFS anytime soon?!

On Wed, Jun 11, 2008 at 7:56 PM, Eric Sandeen <sandeen at redhat.com> wrote:

> Callum Lerwick wrote:
>
> > 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.
>
> Filesystem corruption can happen for many reasons, and journaling cannot
> save you from them all.  Think  about bad cables, memory, kernel bugs,
> bad hardware, rogue writes to the block device, etc.  Journaling doesn't
> help you in the face of any of these problems.  If you are talking about
> data corruption, it could have been an application bug for example (did
> a photo editor corrupt it when you wrote the edited version?)  There is
> a long line of things which can go wrong, unfortunately.  Trusting
> journalling to keep all your data safe now and forevermore is misguided.
>
> > (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.
>
> True, corruption from out-of-order writes due to lack of barriers is
> hard to identify as such.  But unfortunately there are a few other
> things that could have gone wrong too.  There are things in the works to
> help on the integrity front, though (see
> http://oss.oracle.com/projects/data-integrity/ for example).
>
> -Eric
>
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