On Thu, 2020-07-09 at 12:56 -0700, Eric Sandeen 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.

but I use raid-1 on all my disks (since a catastrophic failure 20 years
ago) and that shielded me from all disk failures since then (although I
may have had silent corruption during the years I never lost any really
important data that way, some picture may have got lost that way
probably but it has been inconsequential for me).

However I have had bad kernels, power outages, loss of battery power
(laptops on too long suspend) and other random reasons to force reboot
a system. That has been the primary case of file system checks through
my Fedora usage. And luckily so far I never had a loss of filesystem or
data that way, fsck always ended up solving most of the issues, and
whenever I lost file they ended up being temporary files I did not care

I do not think those failures are common in Facebook fleets, so I am
quite skeptical FB data and failure modes are representative of Fedora
usage as a desktop/laptop OS and therefore of the behavior of btrfs in
those cases.

Note, not saying btrfs should be avoided or anything, just that we need
more data about those failure modes and how they affect btrfs before a
change of defaults.

My 2c,

Simo Sorce
RHEL Crypto Team
Red Hat, Inc

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