Thanks a lot to all who replied! I learned a lot from this thread.
However, what I learned has made me even more doubtful that a btrfs RAID is the
right choice for me at this moment.
There seems to be much uncertainty about the real state (experimental, stable,
production-ready, mature, ...) of btrfs'
raid implementation, even on this very well informed lists.
I really want to have the checksumming and auto-repair feature of btrfs. That
was the original reason why I did't go
with a dmraid in the first place. So there are basically two options left,
btrfs, with a raid 10 or zfs with some raid
10 or 5 equivalent.
zfs seems to be nice, mature solution, but I also prefer to use something
native to Linux.
Best Regards,
Florian
Am 29.11.2016 um 18:20 schrieb Florian Lindner:
> Hello,
>
> I have 4 harddisks with 3TB capacity each. They are all used in a btrfs RAID
> 5. It has come to my attention, that there
> seem to be major flaws in btrfs' raid 5 implementation. Because of that, I
> want to convert the the raid 5 to a raid 10
> and I have several questions.
>
> * Is that possible as an online conversion?
>
> * Since my effective capacity will shrink during conversions, does btrfs
> check if there is enough free capacity to
> convert? As you see below, right now it's probably too full, but I'm going to
> delete some stuff.
>
> * I understand the command to convert is
>
> btrfs balance start -dconvert=raid10 -mconvert=raid10 /mnt
>
> Correct?
>
> * What disks are allowed to fail? My understanding of a raid 10 is like that
>
> disks = {a, b, c, d}
>
> raid0( raid1(a, b), raid1(c, d) )
>
> This way (a XOR b) AND (c XOR d) are allowed to fail without the raid to fail
> (either a or b and c or d are allowed to fail)
>
> How is that with a btrfs raid 10?
>
> * Any other advice? ;-)
>
> Thanks a lot,
>
> Florian
>
>
> Some information of my filesystem:
>
> # btrfs filesystem show /
> Label: 'data' uuid: 57e5b9e9-01ae-4f9e-8a3d-9f42204d7005
> Total devices 4 FS bytes used 7.57TiB
> devid 1 size 2.72TiB used 2.72TiB path /dev/sda4
> devid 2 size 2.72TiB used 2.72TiB path /dev/sdb4
> devid 3 size 2.72TiB used 2.72TiB path /dev/sdc4
> devid 4 size 2.72TiB used 2.72TiB path /dev/sdd4
>
> # btrfs filesystem df /
> Data, RAID5: total=8.14TiB, used=7.56TiB
> System, RAID5: total=96.00MiB, used=592.00KiB
> Metadata, RAID5: total=12.84GiB, used=11.06GiB
> GlobalReserve, single: total=512.00MiB, used=0.00B
>
> # df -h
> Filesystem Size Used Avail Use% Mounted on
>
> /dev/sda4 11T 7.6T 597G 93% /
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