Re: octopus rbd cluster just stopped out of nowhere (>20k slow ops)

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On Di, 2022-12-06 at 15:38 +0100, Boris Behrens wrote:
> I've cross checked the other 8TB disks in our cluster, which are around
> 30-50% with roughly the same IOPs.
> Maybe I am missing some optimization, that is done on the centos7 nodes,
> but not on the ubuntu20.04 node. (If you know something from the top of
> your head, I am happy to hear it).
> Maybe it is just another measuring on ubuntu.

the very first thing I would check is the drive read/write caches:

https://docs.ceph.com/en/quincy/start/hardware-recommendations/#write-caches

(this part of the docs also applies to earlier ceph releases, but wasn't available
in older releases)

I'd recommend installing the udev rule which switches write caches off.

You might want to evaluate first if your drives perform better or worse without caches.

IIRC there where some reports on this ML that performance was even worse on some drives without the cache for certain workloads.

But I never experienced this myself.

HTH

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