On Tue, Feb 02, 2016 at 03:16:40PM +0100, Marco Lorenzo Crociani wrote: > Hi, > df on btrfs RAID1 fs on 3 disks (they are RAID0 hardware, two disk, > arrays but its not important right?) show wrong avail space when > empty > > # uname -a > Linux kvm4.prisma 4.4.0-2.el7.elrepo.x86_64 #1 SMP Tue Jan 26 > 13:06:01 EST 2016 x86_64 x86_64 x86_64 GNU/Linux > > # btrfs --version > btrfs-progs v4.4 > > # btrfs fi show > Label: 'data' uuid: 4421464d-479c-44c4-9f01-8df0f7d05bd2 > Total devices 3 FS bytes used 640.00KiB > devid 1 size 7.28TiB used 2.00GiB path /dev/sdb > devid 2 size 7.28TiB used 2.01GiB path /dev/sdc > devid 3 size 7.28TiB used 2.01GiB path /dev/sdd > > # btrfs fi df /data > Data, RAID1: total=1.00GiB, used=512.00KiB > System, RAID1: total=8.00MiB, used=16.00KiB > Metadata, RAID1: total=2.00GiB, used=112.00KiB > GlobalReserve, single: total=16.00MiB, used=0.00B > > > I expect to get from df -h some like > Filesystem Size Used Avail Use% Mounted on > /dev/sdb 11T 17M 11T 1% /data > but I get: > Filesystem Size Used Avail Use% Mounted on > /dev/sdb 11T 17M 7,3T 1% /data
I've noticed this kind of error, too, although not to such a great degree. The space estimation is definitely broken, although not to such a bad degree as it used to be. There's a relatively complex (but implementable) algorithm that can be used to determine the remaining usable space quite precisely. I'm guessing that that's not in use here. :) I'll try to dig out the actual formula this evening and post it to the list for reference. (It's the formula that's used in the btrfs-usage tool[1], if anyone wants to see the JavaScript implementation). Hugo. [1] http://carfax.org.uk/btrfs-usage/ > If I fill the fs > > # ls -laht > totale 11T > -rw-r--r--. 1 root root 921G 1 feb 16.17 prova10 > drwxr-xr-x. 1 root root 134 1 feb 15.23 . > -rw-r--r--. 1 root root 1,0T 1 feb 14.00 prova9 > -rw-r--r--. 1 root root 1,0T 1 feb 13.07 prova8 > -rw-r--r--. 1 root root 1,0T 1 feb 12.20 prova7 > -rw-r--r--. 1 root root 1,0T 28 gen 21.50 prova6 > -rw-r--r--. 1 root root 1,0T 28 gen 21.08 prova5 > -rw-r--r--. 1 root root 1,0T 28 gen 20.28 prova4 > -rw-r--r--. 1 root root 1,0T 28 gen 19.50 prova3 > -rw-r--r--. 1 root root 1,0T 28 gen 19.13 prova2 > -rw-r--r--. 1 root root 1,0T 28 gen 18.37 prova1 > -rw-r--r--. 1 root root 1,0T 28 gen 18.02 prova0 > dr-xr-xr-x. 18 root root 4,0K 28 gen 15.30 .. > > I get: > > Filesystem Size Used Avail Use% Mounted on > /dev/sdb 11T 11T 256K 100% /data > > # btrfs fi df /data/ > Data, RAID1: total=10.90TiB, used=10.90TiB > System, RAID1: total=8.00MiB, used=1.50MiB > Metadata, RAID1: total=13.00GiB, used=11.24GiB > GlobalReserve, single: total=512.00MiB, used=0.00B > -- Hugo Mills | "He's a nutcase, you know. There's no getting away hugo@... carfax.org.uk | from it -- he'll end up with a knighthood" http://carfax.org.uk/ | PGP: E2AB1DE4 | Lexy, The League of Gentlemen
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