Hi Boris,
PGs are roughtly 35GB.
that's not huge. You wrote you drained one OSD which helped with the
flapping, so you don't have flapping OSDs anymore at all?
If you have identified problematic PGs, you can get the OSD mapping like this:
ceph pg map 26.7
osdmap e14121 pg 26.7 (26.7) -> up [2,5,8] acting [2,5,8]
Just curiously I've checked my pg size which is like 150GB, when are
we talking about big pgs?
That depends on a couple of factors. Just one example from a customer
cluster: They had 240 HDD OSDs with roughly 1 PB a couple of months
ago, which resulted in PG sizes around 400 GB. This led to very long
deep-scrubs, utilizing the OSDs for quite some time, with a noticable
impact on their application. This was not only a performance issue but
also a balancing issue: if the OSDs deviate by only 5 PGs that makes a
difference of 2 TB, on 8 TB disks that is 25% which can quickly bring
the OSDs to or above 85% usage.
That's why we quadrupled the PGs for the main pool which improved
balancing a lot, and deep-scrubs per PG also run much faster with the
cost of having more PGs to scrub, of course.
Zitat von "Szabo, Istvan (Agoda)" <Istvan.Szabo@xxxxxxxxx>:
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
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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?
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