Hi Aand,
Anand Jain wrote on 2015/09/14 17:44 +0800:
Hi Qu,
Unfortunately, single mode means no duplication.
And degrade mount only works for RAID level with
duplication(DUP,RAID1/5/6/10).
further to the below commit.
commit 95669976bd7d30ae265db938ecb46a6b7f8cb893
Btrfs: don't consider the missing device when allocating new chunks
in case of 2-disk RAID1 mounted with only one good disk, we would create
Single profile and actually the created single profiles are still
workable with one disk failed.
Yep, that's the case, and Zhao Lei also found the problem and is still
working on it internally.
But we are doing it in a more flex amd robust method:
No global missing device number check, but do per-chunk check against
its stripes at mount time, to ensure it meets the minimum number for
degradable condition.
So for single/raid0 chunk, they still can't be degraded mounted, if any
of its stripe is missing.
And so the proposed patch below will let
single profile to be mount in this context..
[PATCH 23/23] Btrfs: allow -o rw,degraded for single group profile
to recover when missing disk is replaced balance convert can migrate
single profiles back to RAID1 profile.
Also your explanation for degraded is correct, I am ok to use a new new
mount option (like auto-reduced-profile ?) if needed / confusing.
Sorry for the confusion I caused.
But for above case, IHMO "degraded" is still the proper term.
For 2 disks, 1 missing, single chunk case, if the chunk is in the good
disk, it should be a good chunk, no need to be degraded.
Any comments / feedbacks are welcome.
But for the patch, I'd like to do it in the manner I mentioned:
Check every chunk for whether it's possible to be degraded,
other than current whole fs missing device check.
Thanks,
Qu
Thanks, Anand
--
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
