Re: btrfs balance on single device

[Leonidas Spyropoulos <artafinde@gmail.com>]

On Wed, Dec 18, 2013 at 11:05:29AM +0000, Hugo Mills wrote:
> On Wed, Dec 18, 2013 at 10:44:43AM +0000, Leonidas Spyropoulos wrote:
> > I'm using the same subject as it might be relevant, feel free to change it.#
> > 
> > I'm trying to do some maintenance to the system running over a btrfs file system on root (/). I started a balance on the '/' partition and it failed with the below information:
> > $ sudo btrfs balance start /
> > [sudo] password for inglor:
> > ERROR: error during balancing '/' - No space left on device
> > There may be more info in syslog - try dmesg | tail
> > $ dmesg | tail
> > [93827.115887] btrfs: found 29461 extents
> > [93827.481849] btrfs: relocating block group 29855055872 flags 1
> > [93841.646011] btrfs: found 33171 extents
> > [93851.421207] btrfs: found 33171 extents
> > [93851.782054] btrfs: relocating block group 28781314048 flags 1
> > [93866.815342] btrfs: found 52535 extents
> > [93877.159354] btrfs: found 52534 extents
> > [93877.356805] btrfs: relocating block group 28747759616 flags 34
> > [93880.287185] btrfs: found 1 extents
> > [93880.608798] btrfs: 1 enospc errors during balance
> 
>    You don't specify your kernel version, but if it's older than 3.11
> or so, you should probably upgrade -- 3.10 and earlier had occasional
> bugs where the block reserve system never kept enough blocks free to
> add a new metadata chunk when it was needed, which led to exactly this
> kind of symptom.

You are right, apologies. It is an up to date Archlinux box with a kernel:
$ uname -a
Linux tiamat 3.12.5-1-ARCH #1 SMP PREEMPT Thu Dec 12 12:57:31 CET 2013 x86_64 GNU/Linux

> 
>    Alternatively, and this is a bit of a long shot given that the
> error seems to have been while relocating your system chunk (which
> argues against this particular diagnosis), but:
> 
>    Do you have a large file on that filesystem (larger than 1 GiB)?

Unlikely since the btrfs file system in question is '/' exluding /opt and /media directories (these are other partitions)
$ sudo find / -type f -size +1048576k -and -not -path "/media*" -print
/proc/kcore
find: `/proc/27221/task/27221/fd/5': No such file or directory
find: `/proc/27221/task/27221/fdinfo/5': No such file or directory
find: `/proc/27221/fd/5': No such file or directory
find: `/proc/27221/fdinfo/5': No such file or directory
find: `/run/user/1000/gvfs': Permission denied
inglor@tiamat ~$

> 
>    If so, I would recommend switching to a 3.12 kernel, and running a
> defrag on the file. There's a known and now-fixed bug where you can
> get ENOSPC while balancing, if a file has an extent larger than 1 GiB
> in size. (The bug being that there's an extent over 1 GiB in size in
> the first place).

I might try the defrag option anyway and restart the balance operation, see if this will help anyway.

Thanks,
Leonidas

> 
>    Hugo.
> 
> -- 
> === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk ===
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