On 2016-11-17 15:05, Chris Murphy wrote:
I think the wiki should be updated to reflect that raid1 and raid10
are mostly OK. I think it's grossly misleading to consider either as
green/OK when a single degraded read write mount creates single chunks
that will then prevent a subsequent degraded read write mount. And
also the lack of various notifications of device faultiness I think
make it less than OK also. It's not in the "do not use" category but
it should be in the middle ground status so users can make informed
decisions.
It's worth pointing out also regarding this:
* This is handled sanely in recent kernels (the check got changed from
per-fs to per-chunk, so you still have a usable FS if all the single
chunks are only on devices you still have).
* This is only an issue with filesystems with exactly two disks. If a
3+ disk raid1 FS goes degraded, you still generate raid1 chunks.
* There are a couple of other cases where raid1 mode falls flat on it's
face (lots of I/O errors in a short span of time with compression
enabled can cause a kernel panic for example).
* raid10 has some other issues of it's own (you lose two devices, your
filesystem is dead, which shouldn't be the case 100% of the time (if you
lose different parts of each mirror, BTRFS _should_ be able to recover,
it just doesn't do so right now)).
As far as the failed device handling issues, those are a problem with
BTRFS in general, not just raid1 and raid10, so I wouldn't count those
against raid1 and raid10.
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