Re: btrfs: mixing raid0 and raid1 - How?
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
>
>
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