Re: Scrub: no spae left on device

[Marc MERLIN <marc@merlins.org>]

On Tue, Dec 08, 2015 at 05:24:16PM +0100, Holger Hoffstätte wrote:
> On 12/08/15 17:06, Marc MERLIN wrote:
> > Label: 'btrfs_pool1'  uuid: 5ee24229-2431-448a-868e-2c325d10bfa7
> > 	Total devices 1 FS bytes used 524.26GiB
> > 	devid    1 size 615.01GiB used 614.94GiB path /dev/mapper/pool1
>                         ^^^^^^^^^^^^^^^^^^^^^^^^
> This is what I was alluding to. You could have started a -dusage balance
> *before* the scrub so that one or several data chunks get freed.
> Balancing metadata when you're out of space accomplishes nothing and only
> will very likely fail, just as you saw. You have ~90GB usable space, but
> that space is spread over chunks with low utilisation.

Yes, my partition got a bit full, I freed up space, and unfortunately we
still don't have a background rebalance to fix this, so I did run a manual
one.
But my filesystem was usable, I was writing to it just fine. I was just very
surprised that scrub needed to rewrite blocks on a single disk device.

You could make the case that scrub and balance=0 should be run together.
In the meantime, I upgraded my script:
http://marc.merlins.org/perso/btrfs/2014-03.html#Btrfs-Tips_-Btrfs-Scrub-and-Btrfs-Filesystem-Repair
http://marc.merlins.org/linux/scripts/btrfs-scrub

I figured there is no good reason not to run a balance 20 on metadata and
data every night.

Marc
-- 
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems ....
                                      .... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/