[dropping ceph-users]
On Sat, 10 Oct 2015, wangsongbo wrote:
> Hi all,
> when an osd is marked out, relative IO will be blocked, in which case,
> application built on ceph will fail.According to test result, the larger a
> data is,the longer it will take to elapse.
> How to reduce the impact of this process on the IO?
When you mark an osd out the mon is doing prime_pg_temp, which
preemptively remaps the PG to the same OSDs. This should make peering
fast... except that the OSDs still have to do a cycle of up_thru updates.
Sam, I think we can do the following to avoid this:
- in build prior, we can infer that that interval for last_epoch_start is
also a rw interval (because clearly it finished peering).
- if the acting set and primary do not change, we can skip the up_thru
update (because we will already infer rw from above).
I think the only caveat is that we can only skip the up_thru update
once the entire cluster has a feature bit indicating they understand
that last_epoch_started implies rw.
Anyway, this would mean that there's no subsequent mon interaction after
the mark out (and probably lots of other common scenarios)...
What do you think?
sage
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