You are right. I did the same test with dd. It took a while ;-) 23# dd if=/dev/zero of=file.zero dd: Schreiben in „file.zero“: Auf dem Gerät ist kein Speicherplatz mehr verfügbar 1462670786+0 Datensätze ein 1462670785+0 Datensätze aus 748887441920 Bytes (749 GB) kopiert, 14831,9 s, 50,5 MB/s
24# ll -h insgesamt 698G -rw-r--r-- 1 root root 698G Apr 16 20:03 file.zero Thank you for helping me! Matthias Am 16.04.2016 um 13:35 schrieb Luis Felipe Tabera Alonso: > On sábado, 16 de abril de 2016 12:05:05 (CEST) Matthias Bodenbinder wrote: > >> 38# df -h /mnt/test/ >> Dateisystem Größe Benutzt Verf. Verw% Eingehängt auf >> /dev/sdg 699G 17M 466G 1% /mnt/test > > df is not reliable for btrfs raids, it is better to use btrfs fi df to check > actual used space. > > Using btrfs-tools and kernel from sid (4.4): > > root@mychabol:/mnt/temporal# dd if=/dev/zero of=disk1 bs=1 count=0 seek=750M > root@mychabol:/mnt/temporal# dd if=/dev/zero of=disk2 bs=1 count=0 seek=500M > root@mychabol:/mnt/temporal# dd if=/dev/zero of=disk3 bs=1 count=0 seek=250M > > root@mychabol:/mnt/temporal# mkfs.btrfs -f -draid1 -mraid1 disk1 disk2 disk3 > btrfs-progs v4.4 > See http://btrfs.wiki.kernel.org for more information. > > Label: (null) > UUID: 4fbfda48-3a10-4e1b-92d8-96be759c2a8c > Node size: 16384 > Sector size: 4096 > Filesystem size: 1.46GiB > Block group profiles: > Data: RAID1 83.00MiB > Metadata: RAID1 83.00MiB > System: RAID1 12.00MiB > SSD detected: no > Incompat features: extref, skinny-metadata > Number of devices: 3 > Devices: > ID SIZE PATH > 1 750.00MiB disk1 > 2 500.00MiB disk2 > 3 250.00MiB disk3 > > root@mychabol:/mnt/temporal# losetup /dev/loop0 disk1 > root@mychabol:/mnt/temporal# losetup /dev/loop1 disk2 > root@mychabol:/mnt/temporal# losetup /dev/loop2 disk3 > > root@mychabol:/mnt/temporal# mkdir test > root@mychabol:/mnt/temporal# mount /dev/loop0 test > > root@mychabol:/mnt/temporal# btrfs fi df test/ > Data, RAID1: total=75.00MiB, used=0.00B > System, RAID1: total=8.00MiB, used=16.00KiB > Metadata, RAID1: total=75.00MiB, used=112.00KiB > GlobalReserve, single: total=16.00MiB, used=0.00B > > root@mychabol:/mnt/temporal# df -h test/ > S.ficheros Tamaño Usados Disp Uso% Montado en > /dev/loop0 750M 17M 491M 4% /mnt/temporal/test > > Like in your case, df thinks that there are only 491M usable. However, if I > try to fill the volume > > root@mychabol:/mnt/temporal# cd test/ > root@mychabol:/mnt/temporal/test# dd if=/dev/zero of=file.zero > dd: escribiendo en 'file.zero': No queda espacio en el dispositivo > 1345402+0 registros leídos > 1345401+0 registros escritos > 688845312 bytes (689 MB, 657 MiB) copied, 3,10508 s, 222 MB/s > > root@mychabol:/mnt/temporal/test# ls -lh > total 657M > -rw-r--r-- 1 root root 657M abr 16 13:24 file.zero > root@mychabol:/mnt/temporal/test# df -h . > S.ficheros Tamaño Usados Disp Uso% Montado en > /dev/loop0 750M 674M 64K 100% /mnt/temporal/test > > With the 75M of metadata, you can check that this fills the three devices. > Moreover > > root@mychabol:/mnt/temporal/test# rm file.zero > root@mychabol:/mnt/temporal/test# df -h . > S.ficheros Tamaño Usados Disp Uso% Montado en > /dev/loop0 750M 17M 657M 3% /mnt/temporal/test > > Try to do the same to see if df gets more accurate. > > Still btrfs is quite young, I am not sure if there are serious issues in > 3.17, > I would make some experiments before actual use. > > Bests > > Luis > >
