On Debian Stretch with Linux 4.4.6, btrfs-progs 4.4 in VirtualBox
5.0.16 with 4*2GB VDIs:
# mkfs.btrfs -m raid10 -d raid10 /dev/sdb /dev/sdc /dev/sdd /dev/sdbe
# mount /dev/sdb /mnt
# touch /mnt/test
# umount /mnt
Everything fine so far.
# wipefs -a /dev/sde
*reboot*
# mount /dev/sdb /mnt
mount: wrong fs type, bad option, bad superblock on /dev/sdb,
missing codepage or helper program, or other error
In some cases useful info is found in syslog - try
dmesg | tail or so.
# dmesg | tail
[ 85.979655] BTRFS info (device sdb): disk space caching is enabled
[ 85.979660] BTRFS: has skinny extents
[ 85.982377] BTRFS: failed to read the system array on sdb
[ 85.996793] BTRFS: open_ctree failed
Not very informative! An information regression?
# mount -o degraded /dev/sdb /mnt
# dmesg | tail
[ 919.899071] BTRFS info (device sdb): allowing degraded mounts
[ 919.899075] BTRFS info (device sdb): disk space caching is enabled
[ 919.899077] BTRFS: has skinny extents
[ 919.903216] BTRFS warning (device sdb): devid 4 uuid
8549a275-f663-4741-b410-79b49a1d465f is missing
# touch /mnt/test2
# ls -l /mnt/
total 0
-rw-r--r-- 1 root root 0 mar 25 15:17 test
-rw-r--r-- 1 root root 0 mar 25 15:42 test2
# btrfs device remove missing /mnt
ERROR: error removing device 'missing': unable to go below four
devices on raid10
As expected.
# btrfs replace start -B missing /dev/sde /mnt
ERROR: source device must be a block device or a devid
Would have been nice if missing worked here too. Maybe it does in
btrfs-progs 4.5?
# btrfs replace start -B 4 /dev/sde /mnt
# dmesg | tail
[ 1618.170619] BTRFS info (device sdb): dev_replace from <missing
disk> (devid 4) to /dev/sde started
[ 1618.184979] BTRFS info (device sdb): dev_replace from <missing
disk> (devid 4) to /dev/sde finished
Repaired!
# umount /mnt
# mount /dev/sdb /mnt
# dmesg | tail
[ 1729.917661] BTRFS info (device sde): disk space caching is enabled
[ 1729.917665] BTRFS: has skinny extents
All in all it works just fine with Linux 4.4.6.
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