Booting the VM gave this in the log:
# btrfs balance /
WARNING:
Full balance without filters requested. This operation is very
intense and takes potentially very long. It is recommended to
use the balance filters to narrow down the scope of balance.
Use 'btrfs balance start --full-balance' option to skip this
warning. The operation will start in 10 seconds.
Use Ctrl-C to stop it.
10 9 8 7 6 5 4 3 2 1
Starting balance without any filters.
ERROR: error during balancing '/': Input/output error
There may be more info in syslog - try dmesg | tail
diaspore:~# dmesg | tail
[ 2261.857360] BTRFS info (device sda2): found 144 extents
[ 2261.922014] BTRFS info (device sda2): found 144 extents
[ 2262.003653] BTRFS info (device sda2): found 144 extents
[ 2262.146557] BTRFS info (device sda2): found 144 extents
[ 2262.268034] BTRFS info (device sda2): relocating block group 20951597056 flags data
[ 2268.255631] BTRFS info (device sda2): found 19765 extents
[ 2278.541549] BTRFS info (device sda2): found 19758 extents
[ 2278.685372] BTRFS info (device sda2): relocating block group 14558429184 flags data
[ 2278.714483] BTRFS warning (device sda2): csum failed root -9 ino 269 off 65150976 csum 0x27374190 expected csum 0x7091fbbc mirror 1
[ 2278.714619] BTRFS warning (device sda2): csum failed root -9 ino 269 off 65150976 csum 0x27374190 expected csum 0x7091fbbc mirror 1
Booting from a rescue DVD, then checking with an unmounted /dev/sda2 nothing is wrong:
localhost:~ # btrfs check /dev/sda2
Checking filesystem on /dev/sda2
UUID: 23d33d0f-0468-4408-b73c-b0eec9387d82
checking extents
checking free space cache
checking fs roots
checking csums
checking root refs
checking quota groups
found 6460166144 bytes used, no error found
total csum bytes: 5795704
total tree bytes: 214171648
total fs tree bytes: 193740800
total extent tree bytes: 12910592
btree space waste bytes: 40754145
file data blocks allocated: 35720101888
referenced 11352182784
Both had the same version:
# btrfs version
btrfs-progs v4.13
If I ever need recovery, then these links likely help:
–jeroen