Thank you all for your answers, this was really helpful!
Stefan Priebe wrote:
> yes we have the same issues and switched to seagate for those reasons.
> you can fix at least a big part of it by disabling the write cache of
> those drives - generally speaking it seems the toshiba firmware is
> broken.
> I was not able to find a newer one.
Good to know that we're not alone :) I also looked for a newer firmware, to no
avail.
Igor Fedotov wrote:
> Benoit, wondering what are the write cache settings in your case?
>
> And do you see any difference after disabling it if any?
Write cache is enabled on all our OSDs (including the HGST drives that don't
have a latency issue).
To see if disabling write cache on the Toshiba drives would help, I turned it
off on all 12 drives in one of our OSD nodes:
```
for disk in /dev/sd{a..l}; do hdparm -W0 $disk; done
```
and left it on in the remaining nodes. I used `rados bench write` to create
some load on the cluster, and looked at
```
avg by (hostname) (ceph_osd_commit_latency_ms * on (ceph_daemon) group_left (hostname) ceph_osd_metadata)
```
in Prometheus. The hosts with write cache _enabled_ had a commit latency around
145ms, while the host with write cache _disabled_ had a commit latency around
25ms. So it definitely helps!
Mark Nelson wrote:
> This isn't the first time I've seen drive cache cause problematic
> latency issues, and not always from the same manufacturer.
> Unfortunately it seems like you really have to test the drives you
> want to use before deploying them them to make sure you don't run into
> issues.
That's very true! Data sheets and even public benchmarks can be quite
deceiving, and two hard drives that seem to have similar performance profiles
can perform very differently within a Ceph cluster. Lesson learned.
Cheers,
--
Ben
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