Ahh! did btrfs just explode on me?

[Chris Murphy]

On Wed, Jan 21, 2015 at 12:28 PM, Neal Becker <ndbecker2 at gmail.com> wrote:

>> You should do three things: if the fs is still mounted, update your
>> backup; then install kernel 3.18.3 from updates-testing repo; then use
>> btrfs check --repair using btrfs-progs 3.18.
>>
>
> This is on root fs, btrfs check --repair can't be used on a mounted fs, correct?

Correct. Btrfs won't even let you do a check (read only) on a mounted
fs. Both xfs and ext have options to repair an ro mounted file system,
both admonish this practice and consider it dangerous.

>
>> Since 3.17.8 didn't get this patch, and 3.17 is EOL, it won't ever get
>> it. Looks like the patch is in 3.18.3, and 3.14.29. And it's easier to
>> go with 3.18.3, which is in updates-testing.
>>
>> Next you should reboot from Fedora 21 live media, and 'dnf upgrade
>> btrfs-progs' so that you have btrfs-progs 3.18.1, which is stable. And
>> use 'btrfs check --repair' in case there are any missing files, this
>> should find it. After this, you'd update the backup again in case the
>> first one lacks the missing files.
>>
>>
>
> So you're saying to run btrfs check --repair twice? Once after
> installing/rebooting 3.18.3, and then a 2nd time with live media?

Nope, just once is fine. I'm saying two (incremental) backups. One now
in case things go to hell with the repair, which it shouldn't at this
point. And one after the repair in case it recovers missing files.

The kernel update and btrfs check --repair order doesn't really
matter. I would probably reboot 3.17.8 with rd.break=cmdline and see
if that initramfs has btrfs v3.18.1 and if so then I'd go ahead and do
the repair now, reboot -f and keep using 3.17.8. Then upgrade the
kernel.

Of course if you have btrfs-progs 3.18.1 now, but it's not baked into
your 3.17.8 initramfs, then it's easier to just install 3.18.3 which
will cause a new initramfs to be created which will pull in whatever
btrfs-progs you have now, which ought to be 3.18.1 already since it's
stable.



-- 
Chris Murphy