slow OSD brings down the cluster

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On 08/06/2014 10:43 AM, Luis Periquito wrote:
> Hi,
>
> In the last few days I've had some issues with the radosgw in which all
> requests would just stop being served.
>
> After some investigation I would go for a single slow OSD. I just
> restarted that OSD and everything would just go back to work. Every
> single time there was a deep scrub running on that OSD.
>
> This has happened in several different OSDs, running in different
> machines. I currently have 32 OSDs on this cluster, with 4 OSD per host.
>
> First thing is should this happen? A single OSD with issues/slowness
> shouldn't bring the whole cluster to a crawl...
>

So, it's not the whole cluster which is slow, but the RGW is requesting 
objects which are in a PG where that OSD is currently primary for.

For you it seems like the whole cluster is down, but it's just 'bad 
luck' in this case.

Have you checked if there is anything wrong with the backing disk? 100% 
busy? Read errors?

You can also simply mark the osd as 'out' leave it out of the cluster. 
Re-format the whole OSD and see if it comes back.

Are you using btrfs by any chance?

Wido

> How can I make it stop happening? What kind of debug information can I
> gather to stop this from happening?
>
> any further thoughts?
>
> I'm still running Emperor (0.72.2).
>
> --
>
> Luis Periquito
>
> Unix Engineer
>
>
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-- 
Wido den Hollander
42on B.V.
Ceph trainer and consultant

Phone: +31 (0)20 700 9902
Skype: contact42on


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