The current ceph recommendation is to use between 100-200 PGs/OSD. Therefore, a large PG is a PG that has more data than 0.5-1% of the disk capacity and you should split PGs for the relevant pool.
A huge PG is a PG for which deep-scrub takes much longer than 20min on HDD and 4-5min on SSD.
Average deep-scrub times (time it takes to deep-scrub) are actually a very good way of judging if PGs are too large. These times roughly correlate with the time it takes to copy a PG.
On SSDs we aim for 200+PGs/OSD and for HDDs for 150PGs/OSD. For very large HDD disks (>=16TB) we consider raising this to 300PGs/OSD due to excessively long deep-scrub times per PG.
Best regards,
=================
Frank Schilder
AIT Risø Campus
Bygning 109, rum S14
________________________________________
From: Szabo, Istvan (Agoda) <Istvan.Szabo@xxxxxxxxx>
Sent: Wednesday, August 14, 2024 12:00 PM
To: Eugen Block; ceph-users@xxxxxxx
Subject: Re: Identify laggy PGs
Just curiously I've checked my pg size which is like 150GB, when are we talking about big pgs?
________________________________
From: Eugen Block <eblock@xxxxxx>
Sent: Wednesday, August 14, 2024 2:23 PM
To: ceph-users@xxxxxxx <ceph-users@xxxxxxx>
Subject: Re: Identify laggy PGs
Email received from the internet. If in doubt, don't click any link nor open any attachment !
________________________________
Hi,
how big are those PGs? If they're huge and are deep-scrubbed, for
example, that can cause significant delays. I usually look at 'ceph pg
ls-by-pool {pool}' and the "BYTES" column.
Zitat von Boris <bb@xxxxxxxxx>:
> Hi,
>
> currently we encouter laggy PGs and I would like to find out what is
> causing it.
> I suspect it might be one or more failing OSDs. We had flapping OSDs and I
> synced one out, which helped with the flapping, but it doesn't help with
> the laggy ones.
>
> Any tooling to identify or count PG performance and map that to OSDs?
>
>
> --
> Die Selbsthilfegruppe "UTF-8-Probleme" trifft sich diesmal abweichend im
> groüen Saal.
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