Summary: 3 drive raid0 btrfs volume, in a VM. There is no data at risk at all.
Purely a test. The volume is pretty much full. I added a larger drive /dev/sde
to the existing btrfs volume; then tried to remove one of the smaller drives.
I'm getting an error removing the device. It seems this should be possible,
e.g. move extents on a failing device to a replacement prior to failure.
This is stock Fedora 18 beta kernel, 3.6.1-1.fc18.x86_64 #1 SMP Mon Oct 8
17:19:09 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
[root@f18v ~]# btrfs device add /dev/sde /mnt
[root@f18v ~]# btrfs fi show
failed to read /dev/sr0
Label: none uuid: 6e96a96e-3357-4f23-b064-0f0713366d45
Total devices 4 FS bytes used 7.52GB
devid 4 size 12.00GB used 0.00 path /dev/sde
devid 3 size 3.00GB used 3.00GB path /dev/sdd
devid 2 size 3.00GB used 2.55GB path /dev/sdc
devid 1 size 3.00GB used 3.00GB path /dev/sdb
[root@f18v ~]# btrfs fi df /mnt
Data, RAID0: total=7.61GB, used=7.51GB
System, RAID1: total=8.00MB, used=4.00KB
Metadata, RAID1: total=460.75MB, used=10.91MB
[root@f18v ~]# btrfs device delete /dev/sdb /mnt
ERROR: error removing the device '/dev/sdb' - No space left on device
[ 570.379652] btrfs: relocating block group 29360128 flags 20
[ 571.739126] btrfs: found 2717 extents
[ 571.761061] btrfs: relocating block group 12582912 flags 1
[ 571.787233] btrfs: relocating block group 4194304 flags 4
[ 571.806878] btrfs: relocating block group 0 flags 2
Some time later (hours), I unmounted, remounted, and see this:
[root@f18v ~]# btrfs fi show
failed to read /dev/sr0
Label: none uuid: 6e96a96e-3357-4f23-b064-0f0713366d45
Total devices 4 FS bytes used 7.52GB
devid 4 size 12.00GB used 460.75MB path /dev/sde
devid 3 size 3.00GB used 2.55GB path /dev/sdd
devid 2 size 3.00GB used 3.00GB path /dev/sdc
devid 1 size 3.00GB used 2.53GB path /dev/sdb
Subsequent attempts cause the same failure, but no new entries in dmesg.
If I try with a different device, there is activity, but after a few seconds,
another failure, similar errors in dmesg:
[root@f18v ~]# btrfs device delete /dev/sdc /mnt
ERROR: error removing the device '/dev/sdc' - No space left on device
[ 2478.017828] btrfs: relocating block group 8955363328 flags 20
[ 2478.059607] btrfs: relocating block group 8686927872 flags 20
[ 2479.405142] btrfs: found 2735 extents
[ 2479.436190] btrfs: relocating block group 8663859200 flags 9
[ 2479.458680] btrfs: relocating block group 8243118080 flags 9
[ 2481.949991] btrfs: found 4 extents
[ 2482.700146] btrfs: found 4 extents
[ 2482.717422] btrfs: relocating block group 20971520 flags 18
[ 2482.733835] btrfs: found 1 extents
User error? Known bug?
Chris Murphy--
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