Re: ERROR: error during balancing '.' - No space left on device

Hugo Mills
2014-03-23T11:47:15Z

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On Sun, Mar 23, 2014 at 12:01:44AM -0700, Marc MERLIN wrote:
> legolas:/mnt/btrfs_pool2# btrfs balance .
> ERROR: error during balancing '.' - No space left on device
> There may be more info in syslog - try dmesg | tail
> [ 8454.159635] BTRFS info (device dm-1): relocating block group 288329039872 flags 1
> [ 8590.167294] BTRFS info (device dm-1): relocating block group 232494465024 flags 1
> [ 9200.801177] BTRFS info (device dm-1): relocating block group 85928706048 flags 1
> [ 9533.830623] BTRFS info (device dm-1): 824 enospc errors during balance
>
> But:
> legolas:/mnt/btrfs_pool2# btrfs fi show `pwd`
> Label: btrfs_pool2 uuid: 6afd4707-876c-46d6-9de2-21c4085b7bed
> Total devices 1 FS bytes used 646.41GiB
> devid 1 size 820.45GiB used 820.45GiB path /dev/mapper/disk2
> Btrfs v3.12
> legolas:/mnt/btrfs_pool2#
> Data, single: total=800.42GiB, used=636.91GiB
> System, DUP: total=8.00MiB, used=92.00KiB
> System, single: total=4.00MiB, used=0.00
> Metadata, DUP: total=10.00GiB, used=9.50GiB

^^^ This is where you're full. There's a block reserve here that
(should be) usable for doing a balance, and it seems to be about 500
MiB or so that's the point at which problems show up.

> Metadata, single: total=8.00MiB, used=0.00
>
> I can't see how I'm full, and now that I can't run balance to fix
> things, this is making things worse.

I think you probably shouldn't be doing a full balance, but a
filtered one:

# btrfs balance start -dusage=5 /mnt/btrfs_pool

which should only try to clean up chunks which have little usage (so
it's much faster to run).

> Kernel is 3.14.
>
> What am I missing?

Not much. We do seem to have a problem with not being able to run
balance in recent kernels under some circumstances -- you're not the
only person who's reported this kind of problem lately.

Hugo.

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