On 2017年08月19日 05:52, Zirconium Hacker wrote:
Ok, so since it's clear now that I need that 5 GB device to be
present... I found the image file. But how do I get BTRFS to
recognize the image as a device?
# losetup -f
Remember the loop*, here use /dev/loop1 as example.
# losetup /dev/loop1 <your image>
# partprobe /dev/loop1
Then you should have /dev/loop1p1
# btrfs dev rescan
If nothing wrong happened, you should be good to go.
Thanks,
Qu
I have zero experience with
multi-device systems. Setting it up as a loop device doesn't fix
mounting, and wipefs doesn't detect the BTRFS magic number, but
printing some of it to console shows it does have real data. Writing
the magic number onto it (it's a copy of the original to be safe)
shows in dump-super, but all other values are zero.
I tried sending the above on my phone earlier but it was detected as a
"virus" because it contained HTML. Whoops.
On Fri, Aug 18, 2017 at 11:00 AM, Chris Murphy <li...@colorremedies.com> wrote:
On Fri, Aug 18, 2017 at 2:47 AM, Zirconium Hacker <jared.e...@gmail.com> wrote:
I vaguely remember following this guide at some point:
http://marc.merlins.org/perso/btrfs/post_2014-05-04_Fixing-Btrfs-Filesystem-Full-Problems.html
-- specifically the "Balance cannot run because the filesystem is
full" part. This may have broken some things?
If you don't do 'btrfs device delete /dev/loop0' or if that command
does not complete, then it's possible to get into the situation you're
in.
Have you ever mounted this file system with -o degraded?
I'm going to guess the history is something like:
1. enospc
2. btrfs dev add
3. some kind of filtered balance, which only causes data block groups
to be moved to the 2nd device
4. 2nd device is physically removed without first 'btrfs dev del'
Zirco's superblock very clearly says num_devices 2, so I'd expect
normal mount to always fail unless both devices are present. Is there
some weird edge case where Btrfs might permit non-degraded mount when
only data bg's are on a 2nd device? And then trouble only happens
later when a balance is done and it goes looking for these bg's? And
then, boom!
--
Chris Murphy
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