On 30-11-15 10:08, Carsten Schmitt wrote:
> Hi all,
>
> I'm running ceph version 0.94.5 and I need to downsize my servers
> because of insufficient RAM.
>
> So I want to remove OSDs from the cluster and according to the manual
> it's a pretty straightforward process:
> I'm beginning with "ceph osd out {osd-num}" and the cluster starts
> rebalancing immediately as expected. After the process is finished, the
> rest should be quick:
> Stop the daemon "/etc/init.d/ceph stop osd.{osd-num}" and remove the OSD
> from the crush map: "ceph osd crush remove {name}"
>
> But after entering the last command, the cluster starts rebalancing again.
>
> And that I don't understand: Shouldn't be one rebalancing process enough
> or am I missing something?
>
Well, for CRUSH this are two different things. First, the weight of the
node goes to 0 (zero), but it's still a part of the CRUSH map.
Say, there are still 5 OSDS on that host, 4 with a weight of X and one
with a weight of zero.
When you remove the OSD, there are only 4 OSDs left, that's a change for
CRUSH.
What you should do in this case. Only remove the OSD from CRUSH and
don't mark it as out.
When the cluster is done you can mark it out, but that won't cause a
rebalance since it's already out of the CRUSH map.
It will still work with the other OSDs to migrate the data since the
cluster knows it had that PG information.
> My config is pretty vanilla, except for:
> [osd]
> osd recovery max active = 4
> osd max backfills = 4
>
> Thanks in advance,
> Carsten
>
>
>
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