The Problem
Originally the btrfs file system is build on multiple disks.
# btrfs filesystem show Label: 'MYBTRFS' uuid: 09138ad8-eb2f-4c7c-aef7-90482a67c45c Total devices 3 FS bytes used 768.00KiB devid 1 size 5.00GiB used 1.52GiB path /dev/xvdb devid 2 size 5.00GiB used 520.00MiB path /dev/xvdc devid 3 size 5.00GiB used 1.51GiB path /dev/xvdd
For some reason one disk is faulty and needs to be replaced.
# btrfs filesystem show Label: 'MYBTRFS' uuid: 09138ad8-eb2f-4c7c-aef7-90482a67c45c Total devices 3 FS bytes used 768.00KiB devid 1 size 5.00GiB used 1.52GiB path /dev/xvdb devid 3 size 5.00GiB used 1.51GiB path /dev/xvdd *** Some devices missing
The Solution
1. Mount the btrfs with “-o degraded” option from existing good volume:
# mount -o degraded /dev/xvdd /mnt/btrfs
2. Replace the absent disk with the missing one:
# btrfs replace start 2 /dev/xvdc /mnt/btrfs
3. Balance the file system:
# btrfs filesystem balance
If any error, please check the output of “dmesg”. You may also need to contact your support team if there are errors in dmesg.