On 2016-01-05 08:04, David Goodwin wrote:
Using btrfs progs 4.3.1 on a Vanilla kernel.org 4.1.15 kernel.
time btrfs device delete /dev/xvdh /backups
real 13936m56.796s
user 0m0.000s
sys 1351m48.280s
(which is about 9 days).
Where :
/dev/xvdh was 120gb in size.
OK, based on the device names, you're running this inside a Xen instance
with para-virtualized storage drivers (or Amazon EC2, which is the same
thing at it's core), and that will have at least some impact on
performance (although it will be less impact than if you were using full
virtualization). If you have administrative access to Domain 0, and can
afford to have the VM down, I would suggest checking how long the
equivalent operation takes from Domain 0 (note that to properly check
this, you would need to re-add the device to the FS, re-balance the FS,
and then delete the device). If you get similar results in Domain 0 and
in the VM, then that rules out virtualization as the bottleneck (for
para-virtualized storage backed by physical block devices on the local
system (as opposed to files, or networked block devices), you should see
at most a 10% performance gain running it in Domain 0 assuming both the
VM and Domain 0 have the same number of VCPU's and same amount of RAM).
/backups is a single / "raid 0" volume that now looks like :
Label: 'BACKUP_BTRFS_SNAPS' uuid: 6ee08c31-f310-4890-8424-b88bb77186ed
Total devices 3 FS bytes used 301.09GiB
devid 1 size 100.00GiB used 90.00GiB path /dev/xvdg
devid 3 size 220.00GiB used 196.06GiB path /dev/xvdi
devid 4 size 221.00GiB used 59.06GiB path /dev/xvdj
There are about 400 snapshots on it.
This may be part of the issue. Assuming that /dev/xvdh was mostly full
like /dev/xvdg and /dev/xvdi are now, then that would mean it would take
longer to remove from the filesystem, because all the chunks that are
partially on the device being removed need to be moved to another
device. On top of that, whenever a chunk moves, metadata needs to be
updated, which means a lot of updates if you have a lot of shared
extents, which I'm assuming is the case based on the number of snapshots.
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
