On Thu, Jul 9, 2020 at 1:57 PM Eric Sandeen <sand...@redhat.com> wrote:
> On 7/9/20 2:11 PM, Josef Bacik wrote:
> >>
> >>  From what I've gathered from these responses, btrfs is unique in that it 
> >> is
> >> /expected/ that if anything goes wrong, the administrator should be 
> >> prepared
> >> to scrape out remaining data, re-mkfs, and start over.  If that's 
> >> acceptable
> >> for the Fedora desktop, that's fine, but I consider it a risk that should 
> >> not
> >> be ignored when evaluating this proposal.
> >>
> >
> > Agreed, it's the very first thing I said when I was asked what are the 
> > downsides.  There's clearly more work to be done in the recovery arena.  
> > How often do disks fail for Fedora?  Do we have that data?  Is this a real 
> > risk? Nobody can say because Fedora doesn't have data.
> But again, let me reiterate that disk failures are far from the only
> reason that admins need capable filesystem repair tools, in general.
> We see users running fsck all the time, for various reasons.  I can't
> back it up, but my hunch is that bugs and misconfigurations (i.e. write
> cache) are more often the root cause for filesystem inconsistencies.
> IMHO, focusing on physical disk failure rates is focusing too narrowly,
> but I suppose I'm just joining the chorus of hunches and anecdotes now.

Actually there's quite a lot of evidence of this, even though there's
no precise estimate - not least of which these populations are
constantly dying and reemerging, and can be batch (firmware version)
specific. This is only the most recent such story on linux-btrfs@ (and
warning, this reads like an alien autopsy):


fsck.btrfs is a no op, same as fsck.xfs. And recently the actual
repair utility dissuades users from running it casually.

COW file systems are different. ZFS has no fsck to speak of, it can be
harrassed badly by hardware/firmware bugs too, and yet there aren't
many people who consider ZFS a problemed file system. How would the
story of Btrfs be different either without dm-log-writes to this day,
or had it already arrived in 2010?

Chris Murphy
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