[ceph-users] Slow requests in cache tier with rep_size 2

David Turner drakonstein at gmail.com
Wed Nov 1 07:08:34 PDT 2017


What is your min_size in the cache pool?  If your min_size is 2, then the
cluster would block requests to that pool due to it having too few copies
available.

PS - Please don't consider using rep_size 2 in production.

On Wed, Nov 1, 2017 at 5:14 AM Eugen Block <eblock at nde.ag> wrote:

> Hi experts,
>
> we have upgraded our cluster to Luminous successfully, no big issues
> so far. We are also testing cache tier with only 2 SSDs (we know it's
> not recommended), and there's one issue to be resolved:
>
> Evertime we have to restart the cache OSDs we get slow requests with
> impacts on our client VMs. We never restart both SSDs at the same
> time, of course, so we are wondering why the slow requests? What
> exactly is happening with a replication size of 2? We assumed that if
> one SSD is restarted the data is still available on the other disc, we
> didn't expect any problems. But this occurs everytime we have to
> restart them. Can anyone explain what is going on there? We could use
> your expertise on this :-)
>
> Best regards,
> Eugen
>
> --
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