Matthew Jurgens wrote on 2015/12/19 21:38 +1100:
I've create a subvolume
CMD: btrfs quota enable /export/shared
CMD: btrfs subvol create /export/shared/TV/files
Create subvolume '/export/shared/TV/files'
CMD: btrfs quota rescan /export/shared/TV/files
I've assigned a small quota to it:
CMD: btrfs qgroup limit 100M /export/shared/TV/files
I've also disabled copy on write:
CMD: chattr -R -V +C /export/shared/TV/files
chattr 1.42.12 (29-Aug-2014)
Flags of /export/shared/TV/files set as ---------------C
CMD: sync; btrfs qgroup show -r /export/shared/TV/files
qgroupid rfer excl max_rfer
-------- ---- ---- --------
0/5 2.11TiB 2.11TiB none
0/1894 16.00KiB 16.00KiB 100.00MiB
I created one file until I exceeded the quota using:
CMD: dd if=/dev/zero of=/export/shared/TV/files/junk1 count=50 bs=1M
CMD: dd if=/dev/zero of=/export/shared/TV/files/junk1 count=50 bs=1M
dd: error writing ‘/export/shared/TV/files/junk1’: Disk quota exceeded
50+0 records in
49+0 records out
51380224 bytes (51 MB) copied, 0.0238218 s, 2.2 GB/s
then I removed the file
CMD: rm /export/shared/TV/files/junk1
I tried to create it again (and only got 900k written before the quota
was exceeded):
CMD: dd if=/dev/zero of=/export/shared/TV/files/junk1 count=50 bs=1M
dd: error writing ‘/export/shared/TV/files/junk1’: Disk quota exceeded
1+0 records in
0+0 records out
917504 bytes (918 kB) copied, 0.000568984 s, 1.6 GB/s
then I removed the file
CMD: rm /export/shared/TV/files/junk1
I tried to create it again (and this time got 900k again written before
the quota was exceeded):
dd if=/dev/zero of=/export/shared/TV/files/junk1 count=50 bs=1M
dd: error writing ‘/export/shared/TV/files/junk1’: Disk quota exceeded
1+0 records in
0+0 records out
917504 bytes (918 kB) copied, 0.000943652 s, 972 MB/s
The usage looks ok:
CMD: sync; btrfs qgroup show -r /export/shared/TV/files
qgroupid rfer excl max_rfer
-------- ---- ---- --------
0/5 3.10TiB 3.10TiB none
0/1894 912.00KiB 912.00KiB 100.00MiB
The excl/rfer numbers will always be accurate, as that what 4.2 quota
rework does.
But I can not create any more files:
CMD: dd if=/dev/zero of=/export/shared/TV/files/junk1 count=50 bs=1M
dd: failed to open ‘/export/shared/TV/files/junk1’: Disk quota exceeded
That's what exactly I fixed in 4.3-rc1.
And the operation to trigger the bug is almost the same with xfstest
test case: btrfs/099.
Btrfs doesn't handle quota reserved space well, and caused reserved
space leak. (fixed in 4.3-rc1, but more test would be better)
As long as you did overwrite, no matter whether you enabled or disabled
CoW, it will leak reserved space, and the reserved space won't be freed.
Finally eating up your quota space.
You can either try latest 4.3-rc, which does not only include the quota
fix, but also a lot of delayed ref fixes.
Or, there is a workaround:
Umount the fs and mount it again.
This will free the leaked space and make it work again for a short time,
until your next overwrite.
Thanks,
Qu
CMD: lsattr /export/shared/TV/files
---------------C /export/shared/TV/files/junk1
During other tests I have managed to get it to the point where I can't
delete the file (since disk quota exceeded).
I've waited many minutes to ensure commits etc. The only way I can
seemingly consistently get the ability to write to the directory again
is to reboot. Immediately after a reboot I can create files as expected.
It seems like copy on write is still functioning for this directory? or
quota results have delays?
I've tried mounting the subvolume to another location, but same results.
Is this happening because quotas are not yet considered stable?
Is there something I am doing wrong?
Other Info:
The fstab entry:
LABEL=SHARED /export/shared btrfs
defaults,compress=lzo,relatime,nofail 0 1
uname -a
Linux gw.lambert.rd.to 4.2.7-200.fc22.x86_64 #1 SMP Thu Dec 10 03:28:47
UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
btrfs --version
btrfs-progs v4.2.2
btrfs fi show
Label: 'SHARED' uuid: 199672d4-69ef-4ecf-865a-851bed0167d5
Total devices 5 FS bytes used 3.10TiB
devid 1 size 2.73TiB used 1.27TiB path /dev/sdc
devid 2 size 2.73TiB used 1.27TiB path /dev/sdf
devid 3 size 2.73TiB used 1.27TiB path /dev/sdh
devid 4 size 2.73TiB used 1.27TiB path /dev/sde
devid 5 size 2.73TiB used 1.27TiB path /dev/sdd
btrfs fi df /export/shared
Data, RAID10: total=3.16TiB, used=3.09TiB
System, RAID10: total=64.00MiB, used=352.00KiB
Metadata, RAID10: total=9.00GiB, used=7.61GiB
GlobalReserve, single: total=512.00MiB, used=0.00B
dmesg:
http://edcint.co.nz/tmp/dmesg_20151219.log
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