30 Apr
2024
30 Apr
'24
6 p.m.
Thank you Frank for sharing such valuable experience! I really appreciate
it.
We observe similar timelines: it took more than 1 week to drain our OSD.
Regarding export PGs from failed disk and inject it back to the cluster, do
you have any documentations? I find this online Ceph.io — Incomplete PGs --
OH MY! <https://ceph.io/en/news/blog/2015/incomplete-pgs-oh-my/>, but not
sure whether it's the standard process.
Thanks,
Mary
On Tue, Apr 30, 2024 at 3:27 AM Frank Schilder <frans(a)dtu.dk> wrote:
Hi all,
I second Eugen's recommendation. We have a cluster with large HDD OSDs
where the following timings are found:
- drain an OSD: 2 weeks.
- down an OSD and let cluster recover: 6 hours.
The drain OSD procedure is - in my experience - a complete waste of time,
actually puts your cluster at higher risk of a second failure (its not
guaranteed that the bad PG(s) is/are drained first) and also screws up all
sorts of internal operations like scrub etc for an unnecessarily long time.
The recovery procedure is much faster, because it uses all-to-all recovery
while drain is limited to no more than max_backfills PGs at a time and your
broken disk sits much longer in the cluster.
On SSDs the "down OSD"-method shows a similar speed-up factor.
For a security measure, don't destroy the OSD right away, wait for
recovery to complete and only then destroy the OSD and throw away the disk.
In case an error occurs during recovery, you can almost always still export
PGs from a failed disk and inject it back into the cluster. This, however,
requires to take disks out as soon as they show problems and before they
fail hard. Keep a little bit of life time to have a chance to recover data.
Look at the manual of ddrescue why it is important to stop IO from a
failing disk as soon as possible.
Best regards,
=================
Frank Schilder
AIT Risø Campus
Bygning 109, rum S14
________________________________________
From: Eugen Block <eblock(a)nde.ag>
Sent: Saturday, April 27, 2024 10:29 AM
To: Mary Zhang
Cc: ceph-users(a)ceph.io; Wesley Dillingham
Subject: [ceph-users] Re: Remove an OSD with hardware issue caused rgw 503
If the rest of the cluster is healthy and your resiliency is
configured properly, for example to sustain the loss of one or more
hosts at a time, you don’t need to worry about a single disk. Just
take it out and remove it (forcefully) so it doesn’t have any clients
anymore. Ceph will immediately assign different primary OSDs and your
clients will be happy again. ;-)
Zitat von Mary Zhang <maryzhang0920(a)gmail.com>om>:
Thank you Wesley for the clear explanation
between the 2 methods!
The tracker issue you mentioned https://tracker.ceph.com/issues/44400
talks
about primary-affinity. Could primary-affinity
help remove an OSD with
hardware issue from the cluster gracefully?
Thanks,
Mary
On Fri, Apr 26, 2024 at 8:43 AM Wesley Dillingham <wes(a)wesdillingham.com
wrote:
> What you want to do is to stop the OSD (and all its copies of data it
> contains) by stopping the OSD service immediately. The downside of this
> approach is it causes the PGs on that OSD to be degraded. But the
upside is
> the OSD which has bad hardware is immediately
no longer participating
in
> any client IO (the source of your RGW 503s).
In this situation the PGs
go
> into degraded+backfilling
>
> The alternative method is to keep the failing OSD up and in the cluster
> but slowly migrate the data off of it, this would be a long drawn out
> period of time in which the failing disk would continue to serve client
> reads and also facilitate backfill but you wouldnt take a copy of the
data
> out of the cluster and cause degraded PGs. In
this scenario the PGs
would
> be remapped+backfilling
>
> I tried to find a way to have your cake and eat it to in relation to
this
> "predicament" in this tracker
issue:
https://tracker.ceph.com/issues/44400
> but it was deemed "wont fix".
>
> Respectfully,
>
> *Wes Dillingham*
> LinkedIn <http://www.linkedin.com/in/wesleydillingham>
> wes(a)wesdillingham.com
>
>
>
>
> On Fri, Apr 26, 2024 at 11:25 AM Mary Zhang <maryzhang0920(a)gmail.com>
> wrote:
>
>> Thank you Eugen for your warm help!
>>
>> I'm trying to understand the difference between 2 methods.
>> For method 1, or "ceph orch osd rm osd_id", OSD Service — Ceph
>> Documentation
>> <https://docs.ceph.com/en/latest/cephadm/services/osd/#remove-an-osd>
>> says
>> it involves 2 steps:
>>
>> 1.
>>
>> evacuating all placement groups (PGs) from the OSD
>> 2.
>>
>> removing the PG-free OSD from the cluster
>>
>> For method 2, or the procedure you recommended, Adding/Removing OSDs —
>> Ceph
>> Documentation
>> <
>>
https://docs.ceph.com/en/latest/rados/operations/add-or-rm-osds/#removing-o…
>> >
>> says
>> "After the OSD has been taken out of the cluster, Ceph begins
rebalancing
>> the cluster by migrating placement groups
out of the OSD that was
removed.
>> "
>>
>> What's the difference between "evacuating PGs" in method 1 and
"migrating
>> PGs" in method 2? I think method 1
must read the OSD to be removed.
>> Otherwise, we would not see slow ops warning. Does method 2 not involve
>> reading this OSD?
>>
>> Thanks,
>> Mary
>>
>> On Fri, Apr 26, 2024 at 5:15 AM Eugen Block <eblock(a)nde.ag> wrote:
>>
>> > Hi,
>> >
>> > if you remove the OSD this way, it will be drained. Which means that
>> > it will try to recover PGs from this OSD, and in case of hardware
>> > failure it might lead to slow requests. It might make sense to
>> > forcefully remove the OSD without draining:
>> >
>> > - stop the osd daemon
>> > - mark it as out
>> > - osd purge <id|osd.id> [--force] [--yes-i-really-mean-it]
>> >
>> > Regards,
>> > Eugen
>> >
>> > Zitat von Mary Zhang <maryzhang0920(a)gmail.com>om>:
>> >
>> > > Hi,
>> > >
>> > > We recently removed an osd from our Cepth cluster. Its underlying
disk
>> > has
>> > > a hardware issue.
>> > >
>> > > We use command: ceph orch osd rm osd_id --zap
>> > >
>> > > During the process, sometimes ceph cluster enters warning state
with
>> slow
>> > > ops on this osd. Our rgw also failed to respond to requests and
>> returned
>> > > 503.
>> > >
>> > > We restarted rgw daemon to make it work again. But the same failure
>> > occured
>> > > from time to time. Eventually we noticed that rgw 503 error is a
>> result
>> > of
>> > > osd slow ops.
>> > >
>> > > Our cluster has 18 hosts and 210 OSDs. We expect remove an osd with
>> > > hardware issue won't impact cluster performance & rgw
availbility.
Is
>> our
>> > > expectation reasonable? What's the best way to handle osd with
>> hardware
>> > > failures?
>> > >
>> > > Thank you in advance for any comments or suggestions.
>> > >
>> > > Best Regards,
>> > > Mary Zhang
>> > > _______________________________________________
>> > > ceph-users mailing list -- ceph-users(a)ceph.io
>> > > To unsubscribe send an email to ceph-users-leave(a)ceph.io
>> >
>> >
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