Hello,
Sorry for the long email...
I've found my system locks up when scrubbing with 3.18.x, but not with
3.17.8 across 2 systems.
I have the following BTRFS partitions on system 1:
/ (128GiB, 49GiB used on SSD)
/home (4.2TiB, 624GB used on HDD RAID volume)
I have the following BTRFS partitions on system 2:
/ (196GiB, 17GiB used on HDD RAID volume)
/home (7.1TiB, 2.9TiB used on HDD RAID volume)
My OS is Netrunner 15 (which 98% Kubuntu) on system 1, and up-to-date
debian testing on system 2.
I've never encountered a lock up while scrubbing /. Just with /home.
The systems never lock up immediately, but takes some time. VERY rarely
I'll see the lockup when the scrub is at <100GiB completed. Typically it
happens somewhere between 200-350GiB. A few times it's gone beyond
500GiB. This is probably why I've never encountered the issue with /,
it's just not big enough on either system.
Both systems were otherwise idle while performing the scrubs that
crashed the systems.
/home is on a partition on a RAID10 volume on a 3ware 9740-4i controller
with 4x 3TB disks on system 1. On system 2, it's the same controller but
with 4x 4TB disks (and / on system 2 is a partition on the same RAID
volume rather than a separate disk). Both systems have 32GiB memory, and
the otherwise the hardware is pretty different between the systems (AMD
Vs. Intel, etc).
I suspect that the RAID controller probably isn't relevant. Both arrays
and their drives are healthy.
I've also encountered the issue on a freshly formatted filesystem with
my data copied from a backup on system 1.
I've tried tried scrubbing with btrfs-progs 3.17 (installed from the
distribution repos on both systems), and btrfs-progs from git (using tag
v3.18.x). Neither version made a difference.
In case this is helpful to anyone, here's how I've discovered the issue:
I decided to test btrfs with bcache on system 1 to see if the stability
had improved since I'd tried bcache+btrfs about a year ago. I backed up
/home on system 1 and then freshly formatted it and set it to use
bcache. I was running Linux 3.18.8 and encountered the problem that I've
described above. I assumed the bcache+btrfs combination was still broken
so I formatted the system again (this time still using btrfs, but
without bcache) and copied all my files back. I encountered the same
issue without bcache. Realizing the issue wasn't bcache related, I did
ANOTHER format, this time back to bcache+btrfs.
From here in my testing, I found that system 2 (which has no bcache)
also crashed when scrubbing with Linux 3.18.8. I decided to try 3.17.8
on system 1 (since 3.18.8 seemed to be the common denominator between
the 2 systems), found that fixed the issue, and then downgraded system 2
to use 3.17.8 as well, which also fixed the issue there.
(Note: At one point I also tried Linux 3.18.7 and 3.18.5, however, those
kernels are affected by the scrub/crash issue as well.)
I found something else interesting when I tested against Linux 3.19.0.
With 3.19.0, the bcache system always crashes fairly early in the scrub
(<100GiB), but the non-bcache system has no issues. This suggests my
problem with 3.19.0 is a bcache+btrfs issue (or simply an issue with
bcache).
I'm not sure if bcache is relevant to the BTRFS devs at this point, but
I thought I'd put that there for anyone who might find that information
useful.
To summarize:
I've tested with 2 systems, and scrubbing caused crashes occurred on
both with Linux 3.18.8, but not with 3.17.8 for both systems
I've tested 1 system with and without bcache, and bcache made no
difference between Linux 3.17.8 and 3.18.8.
I've tested with 3.19.0, and I crash when scrubbing on the bcache
system, but not the non-bcache system.
Thanks!
-Cameron
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