On Sun, May 14, 2017 at 09:13:35PM +0200, Hans van Kranenburg wrote:
> On 05/13/2017 10:54 PM, Marc MERLIN wrote:
> > Kernel 4.11, btrfs-progs v4.7.3
> >
> > I run scrub and balance every night, been doing this for 1.5 years on this
> > filesystem.
>
> What are the exact commands you run every day?
http://marc.merlins.org/perso/btrfs/post_2014-03-19_Btrfs-Tips_-Btrfs-Scrub-and-Btrfs-Filesystem-Repair.html
(at the bottom)
every night:
1) scrub
2) balance -musage=0
3) balance -musage=20
4) balance -dusage=0
5) balance -dusage=20
> > How did I get into such a misbalanced state when I balance every night?
>
> I don't know, since I don't know what you do exactly. :)
Now you do :)
> > My filesystem is not full, I can write just fine, but I sure cannot
> > rebalance now.
>
> Yes, because you have quite some allocated but unused space. If btrfs
> cannot just allocate more chunks, it starts trying a bit harder to reuse
> all the empty spots in the already existing chunks.
Ok. shouldn't balance fix problems just like this?
I have 60GB-ish free, or in this case that's also >25%, that's a lot
Speaking of unallocated, I have more now:
Device unallocated: 993.00MiB
This kind of just magically fixed itself during snapshot rotation and
deletion I think.
Sure enough, balance works again, but this feels pretty fragile.
Looking again:
Device size: 228.67GiB
Device allocated: 227.70GiB
Device unallocated: 993.00MiB
Free (estimated): 58.53GiB (min: 58.53GiB)
You're saying that I need unallocated space for new chunks to be
created, which is required by balance.
Should btrfs not take care of keeping some space for me?
Shoudln't a nigthly balance, which I'm already doing, help even more
with this?
> > Besides adding another device to add space, is there a way around this
> > and more generally not getting into that state anymore considering that
> > I already rebalance every night?
>
> Add monitoring and alerting on the amount of unallocated space.
>
> FWIW, this is what I use for that purpose:
>
> https://packages.debian.org/sid/munin-plugins-btrfs
> https://packages.debian.org/sid/monitoring-plugins-btrfs
>
> And, of course the btrfs-heatmap program keeps being a fun tool to
> create visual timelapses of your filesystem, so you can learn how your
> usage pattern is resulting in allocation of space by btrfs, and so that
> you can visually see what the effect of your btrfs balance attempts is:
That's interesting, but ultimately, users shoudln't have to micromanage
their filesystem to that level, even btrfs.
a) What is wrong in my nightly script that I should fix/improve?
b) How do I recover from my current state?
Thanks,
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
ome page: http://marc.merlins.org/ | PGP 1024R/763BE901
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