On 12/07/16 14:58, Wido den Hollander wrote:
>> Op 7 december 2016 om 11:29 schreef Kees Meijs <kees@xxxxxxxx>:
>>
>>
>> Hi Wido,
>>
>> Valid point. At this moment, we're using a cache pool with size = 2 and
>> would like to "upgrade" to size = 3.
>>
>> Again, you're absolutely right... ;-)
>>
>> Anyway, any things to consider or could we just:
>>
>> 1. Run "ceph osd pool set cache size 3".
>> 2. Wait for rebalancing to complete.
>> 3. Run "ceph osd pool set cache min_size 2".
>>
> Indeed! It is a simple as that.
>
> Your cache pool can also contain very valuable data you do not want to loose.
>
> Wido
Almost as simple as that...
First make sure there is free space. Then when you run it, also monitor
that there are no side effects... bad performance, blocked requests, etc.
And if there are issues, be ready to stop it with:
ceph osd set nobackfill
ceph osd set norecover
And then figure out some tuning... eg. (very minimal settings)
# more than likely you can handle more than 1 on a small cluster and
maybe much more
ceph tell osd.* injectargs --osd_max_backfills=1
# manuals/emails/something I read suggest a number like 0.05 ... I
find that does nothing in times of real trouble, but this really slows
down recovery
ceph tell osd.* injectargs --osd_recovery_sleep=0.6
ceph osd set noscrub
ceph osd set nodeep-scrub
# also I think this one is highly relevant, but not sure what to
suggest for it... others suggest 12[1] to 16[2], and so far I found 8
works better than 12-32 for my frequent "blocked requests" small cluster
# --osd_op_threads=...
And then unset those flags to resume it. And when done, consider
unsetting your new settings (I would unset the noscrub at least).
[1]
https://www.openstack.org/summit/vancouver-2015/summit-videos/presentation/a-year-with-cinder-and-ceph-at-twc
[2] http://www.spinics.net/lists/ceph-users/msg32368.html somewhere in
this thread, but can't find it online "We have recently increase osd op
threads from 2 (default value) to 16 because CPU usage on DN was very
low. We have the impression it has increased overall ceph cluster
performances and reduced block ops occurrences."
--
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