If I remember correctly op-queue-cut-off can't be changed during
runtime, the other two can.
Zitat von Martin Palma <martin@xxxxxxxx>:
To set these setting during runtime I use the following commands from
my admin node:
ceph tell osd.* injectargs '--osd-max-backfills 1'
ceph tell osd.* injectargs '--osd-recovery-max-active 1'
ceph tell osd.* injectargs '--osd-op-queue-cut-off high'
Right?
On Wed, Aug 19, 2020 at 11:08 AM Stefan Kooman <stefan@xxxxxx> wrote:
On 2020-08-19 04:05, norman wrote:
> Hans,
>
> I made a big change in my staging cluster before, I set a pool pg_num
> from 8 to 2048, it cased the cluster available for a long time :(
I doubt it will have that big an effect this time. The change from 8 ->
2048 is way bigger than "just" a doubling to 4096. It of course depends
on how much data has been added to the pool in the meantime. But if the
PGs hold less data per PG, the impact is probably lower.
It's always a tradeoff between recovery speed and decent client IO
performance, and highly dependent per use case, cluster size, hardware
specifications like disk type, amount of RAM / CPU and networking.
For some clusters the values you have used might by no big deal (if you
have hundreds of nodes) but for small(er) clusters this can have a big
impact. Might, if you have NVMe and loads of memory and CPU you might
even get away with it.
So it's best to start with low(est) possible recovery/backfill settings
and slowly scaling up. Having metrics of your cluster and client VMs
(perceived latency on VMs for example) will be crucial to put a number
on this. Having a baseline of the performance of the cluster will help
to decide when things get out of hand. It will also help to identify the
time the cluster is less busy, and use that time window to perform
maintenance (i.e. not when backups are active, which tend to stress
clusters a lot).
Gr. Stefan
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