On 05/05/14 07:50, Marc MERLIN wrote:
On Mon, May 05, 2014 at 06:11:28AM +0200, Brendan Hide wrote:
The "per-device" used amount refers to the amount of space that has
been allocated to chunks. That first one probably needs a balance.
Btrfs doesn't behave very well when available diskspace is so low
due to the fact that it cannot allocate any new chunks. An attempt
to allocate a new chunk will result in ENOSPC errors.
The "Total" bytes used refers to the total actual data that is stored.
Right. So 'Total used' is what I'm really using, whereas 'devid used' is
actually what is being used due to the way btrfs doesn't seem to reclaim
chunks after they're not used anymore, or some similar problem.
In the second FS:
Label: btrfs_pool1 uuid: 4850ee22-bf32-4131-a841-02abdb4a5ba6
Total devices 1 FS bytes used 442.17GiB
devid 1 size 865.01GiB used 751.04GiB path /dev/mapper/cryptroot
The difference is huge between 'Total used' and 'devid used'.
Is btrfs going to fix this on its own, or likely not and I'm stuck doing
a full balance (without filters since I'm balancing data and not
metadata)?
If that helps.
legolas:~# btrfs fi df /mnt/btrfs_pool1
Data, single: total=734.01GiB, used=435.29GiB
System, DUP: total=8.00MiB, used=96.00KiB
System, single: total=4.00MiB, used=0.00
Metadata, DUP: total=8.50GiB, used=6.74GiB
Metadata, single: total=8.00MiB, used=0.00
Thanks,
Marc
What I typically do in snapshot cleanup scripts is to use the usage=
filter with the percentage being a simple algorithm of "halfway between
actual data and maximum chunk allocation I'm comfortable with". As an
example, one of my servers' diskspace was at 65% and last night the
chunk allocation reached the 90% mark. So it automatically ran the
balance with "dusage=77". This would have cleared out about half of the
"unnecessary" chunks.
Balance causes a lot of load with spinning rust - of course,
after-hours, nobody really cares. With SSDs it causes wear. This is just
one method I felt was a sensible way for me to avoid ENOSPC issues while
also ensuring I'm not rebalancing the entire system unnecessarily.
--
__________
Brendan Hide
http://swiftspirit.co.za/
http://www.webafrica.co.za/?AFF1E97
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