Hi, I use qgroups for subvolumes in Rockstor and have been noticing this behavior for a while(at least from 3.18 days). The behavior is that I get "Disk quota exceeded" errors before even hitting 70% usage. Here's a simple demonstration of the problem.
[root@rock-dev ~]# btrfs fi show singlepool Label: 'singlepool' uuid: 77eb22bf-5f07-4f7e-83af-da183ceccd4d Total devices 1 FS bytes used 224.00KiB devid 1 size 3.00GiB used 276.00MiB path /dev/sdab btrfs-progs v4.1.2 [root@rock-dev ~]# btrfs subvol list -p /mnt2/singlepool/ ID 257 gen 9 parent 5 top level 5 path singleshare1 [root@rock-dev ~]# btrfs qgroup show -pcre /mnt2/singlepool qgroupid rfer excl max_rfer max_excl parent child -------- ---- ---- -------- -------- ------ ----- 0/5 16.00KiB 16.00KiB none none --- --- 0/257 16.00KiB 16.00KiB none none 2015/1 --- 2015/1 16.00KiB 16.00KiB 1.00GiB none --- 0/257 As you can see, the subvolume is part of the 2015/1 qgroup with a 1GiB max_rfer limit. Now I start writing to the it. [root@rock-dev ~]# dd if=/dev/urandom of=/mnt2/singleshare1/file.1 bs=1M count=256; sync 256+0 records in 256+0 records out 268435456 bytes (268 MB) copied, 15.5902 s, 17.2 MB/s [root@rock-dev ~]# btrfs fi df /mnt2/singlepool/ Data, single: total=328.00MiB, used=256.12MiB System, single: total=4.00MiB, used=16.00KiB Metadata, single: total=264.00MiB, used=432.00KiB GlobalReserve, single: total=16.00MiB, used=0.00B [root@rock-dev ~]# btrfs qgroup show -pcre /mnt2/singlepool qgroupid rfer excl max_rfer max_excl parent child -------- ---- ---- -------- -------- ------ ----- 0/5 16.00KiB 16.00KiB none none --- --- 0/257 256.02MiB 256.02MiB none none 2015/1 --- 2015/1 256.02MiB 256.02MiB 1.00GiB none --- 0/257 [root@rock-dev ~]# dd if=/dev/urandom of=/mnt2/singleshare1/file.2 bs=1M count=256; sync 256+0 records in 256+0 records out 268435456 bytes (268 MB) copied, 15.7899 s, 17.0 MB/s [root@rock-dev ~]# btrfs fi df /mnt2/singlepool/ Data, single: total=648.00MiB, used=512.19MiB System, single: total=4.00MiB, used=16.00KiB Metadata, single: total=264.00MiB, used=688.00KiB GlobalReserve, single: total=16.00MiB, used=0.00B [root@rock-dev ~]# btrfs qgroup show -pcre /mnt2/singlepool qgroupid rfer excl max_rfer max_excl parent child -------- ---- ---- -------- -------- ------ ----- 0/5 16.00KiB 16.00KiB none none --- --- 0/257 512.02MiB 512.02MiB none none 2015/1 --- 2015/1 512.02MiB 512.02MiB 1.00GiB none --- 0/257 Ok, so far so good. I've written 2 files, 512MiB in total and it's reflected accurately in the qgroup accounting. Now, I write a 3rd 256MiB file. [root@rock-dev ~]# dd if=/dev/urandom of=/mnt2/singleshare1/file.3 bs=1M count=256; sync 256+0 records in 256+0 records out 268435456 bytes (268 MB) copied, 15.6963 s, 17.1 MB/s [root@rock-dev ~]# sync [root@rock-dev ~]# btrfs fi df /mnt2/singlepool/ Data, single: total=968.00MiB, used=768.25MiB System, single: total=4.00MiB, used=16.00KiB Metadata, single: total=264.00MiB, used=944.00KiB GlobalReserve, single: total=16.00MiB, used=0.00B [root@rock-dev ~]# btrfs qgroup show -pcre /mnt2/singlepool qgroupid rfer excl max_rfer max_excl parent child -------- ---- ---- -------- -------- ------ ----- 0/5 16.00KiB 16.00KiB none none --- --- 0/257 662.00MiB 662.00MiB none none 2015/1 --- 2015/1 662.00MiB 662.00MiB 1.00GiB none --- 0/257 I find it odd that the usage shows 662.00Mib, I was expecting to see 768MiB(512+256). Is this because the third 256MiB file was compressed to 150MiB while the first two files were not compressible? Or is it something else, and if so, what is it? If I attempt to write another 256MiB file, i get this error: [root@rock-dev ~]# dd if=/dev/urandom of=/mnt2/singleshare1/file.4 bs=1M count=256; sync dd: failed to open ‘/mnt2/singleshare1/file.4’: Disk quota exceeded If I try to remove one of the three files written successfully, i get the same error: [root@rock-dev ~]# cd /mnt2/singleshare2/ [root@rock-dev singleshare2]# ls file.1 file.2 file.3 [root@rock-dev singleshare2]# ls -l total 786432 -rw-r--r-- 1 root root 268435456 Aug 13 10:49 file.1 -rw-r--r-- 1 root root 268435456 Aug 13 10:50 file.2 -rw-r--r-- 1 root root 268435456 Aug 13 10:50 file.3 [root@rock-dev singleshare2]# rm file.3 rm: remove regular file ‘file.3’? y rm: cannot remove ‘file.3’: Disk quota exceeded I was able to reproduce this behavior with other raid profiles as well and recently, some of Rockstor users have also confirmed it with subvolume sizes small and large. I hope this is not a BTRFS bug and it's something that I am doing wrong. Can someone familiar with qgroups comment on this? I see that there are qgroup related patches going into 4.2. Are these problems addressed by them, perhaps? -- Suman Chakravartula Founder @ Rockstor http://rockstor.com http://rockstor.com/blog http://forum.rockstor.com -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
