[arch-general] can't balance full btrfs raid6 filesystem

[Sebastian Verderber]

---- Jameson Pugh schrieb ----

> On Sat, Feb 20, 2016 at 8:04 AM, Alistair Grant <akgrant0710 at gmail.com> 
> wrote:
> > On 20 February 2016 at 02:38, Jameson Pugh <imntreal at gmail.com> wrote:
> >>  I have a raid6 btrfs filesystem which I filled up, and added a disk 
> >> to:
> >> 
> >>>  sudo btrfs fi show /dev/sdb
> >>  Label: 'raid'  uuid: 96c75e11-ab60-44b6-a450-4cd2831f86f0
> >>         Total devices 5 FS bytes used 917.77GiB
> >>         devid    1 size 465.76GiB used 465.76GiB path /dev/sdb
> >>         devid    2 size 465.76GiB used 465.76GiB path /dev/sdc
> >>         devid    3 size 465.76GiB used 465.76GiB path /dev/sdd
> >>         devid    4 size 931.51GiB used 465.76GiB path /dev/sde
> >>         devid    5 size 1.82TiB used 0.00B path /dev/sdf
> >> 
> >>  Despite having removed files, and added the new device, I still 
> >> can't
> >>  balance the filesystem:
> >> 
> >>  ...
> > 
> > Did you do it in that order?  How about attempting to remove files
> > after adding the new device.
> > 
> > As Guus said, removing a snapshot is more likely to help than 
> > removing files.
> > 
> > If you haven't already done so, I'd also suggest posting this to the
> > linux-btrfs mailing list (see
> > https://btrfs.wiki.kernel.org/index.php/Btrfs_mailing_list)
> 
> Yes. I've tried removing files after adding the device. Unfortunately, 
> there are no snapshots. I could try removing subvolumes. I'll try the 
> btrfs list.

As mentioned before, removing files doesn't solve the problem, and yes, ZFS suffers from the same problem (first hand experience...) As soon as the disk is full the Filesystem is paralysed. The only method that can help is nuking a big file, e.g. an HD movie you don't need or have a backup of. Try this:

echo > /path/to/bloodyhugefile

This reduces the file size to zero and should free enough space for new metadata.

Greets
Sebastian

> Thanks,
> Jameson