Hi,
for a production cluster I'd recommend sticking to wpq at the moment,
where you can apply "legacy" recovery settings. If you're willing to
help the Devs figuring out how to get to the bottom of this, I'm sure
they would highly appreciate it. But I currently know too little about
mclock to know the right knobs. So far I've only tried it with only a
few different settings and none helped significantly.
I would expect that there are existing tracker issues since this topic
comes up every other week or so. If not, I'd suggest to create one.
Thanks,
Eugen
Zitat von "Alex Hussein-Kershaw (HE/HIM)" <alexhus@xxxxxxxxxxxxx>:
Hi Folks,
I'm trying to scale-in a Ceph Cluster. It's running 19.2.0 and is
cephadm managed. It's just a test system, so has basically no data
and only has 3 OSDs.
As part of the scaling-in, I run "ceph orch host drain <hostname>
--zap-osd-devices" as per Host Management — Ceph
Documentation<https://docs.ceph.com/en/reef/cephadm/host-management/#removing-hosts>. That starts off the OSD
draining.
However, that drain seems to take an enormous amount of time. My OSD
has less than 100MiB raw storage, and I let it run for 2 hours over
lunch and it still was not finished, so I cancelled it.
I'm not sure how this scales, but I'm assuming at least linearly
with data stored, which seems like bad news for doing this on real
systems, which may have several TBs per OSD.
I had a look at the recovery profiles documentation here mClock
Config Reference — Ceph
Documentation<https://docs.ceph.com/en/reef/rados/configuration/mclock-config-ref/> which seemed to indicate I could speed this up (but my impression was maybe I could get a speed up of 2x which seems like it will still take an
age).
On the other hand, just switching off the host running the OSD and
doing an offline host removal ("ceph orch host rm <hostname>
--offline") seems much easier, with the trade-off that the Cluster
recovers after the loss of the OSD rather than pre-emptively. But
that big risk of that seems to be mitigated by "ceph orch host
ok-to-stop <hostname>" to check I won't cause any PGs to go offline
before hand.
Are there any tricks here that I'm missing?
Thanks,
Alex
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