On 10/6/2020 1:04 PM, Kristof Coucke wrote:
Another strange thing is going on:
No client software is using the system any longer, so we would expect
that all IOs are related to the recovery (fixing of the degraded PG).
However, the disks that are reaching high IO are not a member of the
PGs that are being fixed.
So, something is heavily using the disk, but I can't find the process
immediately. I've read something that there can be old client
processes that keep on connecting to an OSD for retrieving data for a
specific PG while that PG is no longer available on that disk.
I bet it's rather PG removal happening in background....
Op di 6 okt. 2020 om 11:41 schreef Kristof Coucke
<kristof.coucke@xxxxxxxxx <mailto:kristof.coucke@xxxxxxxxx>>:
Yes, some disks are spiking near 100%... The delay I see with the
iostat (r_await) seems to be synchronised with the delays between
queued_for_pg and reached_pg events.
The NVMe disks are not spiking, just the spinner disks.
I know the rocksdb is only partial on the NVMe. The read-ahead is
also 128kb (os level) (for spinner disks). As we are dealing with
smaller files, this might also lead to a decrease of the performance.
I'm still investigating, but I'm wondering if the system is also
reading from disk for finding the KV pairs.
Op di 6 okt. 2020 om 11:23 schreef Igor Fedotov <ifedotov@xxxxxxx
<mailto:ifedotov@xxxxxxx>>:
Hi Kristof,
are you seeing high (around 100%) OSDs' disks (main or DB ones)
utilization along with slow ops?
Thanks,
Igor
On 10/6/2020 11:09 AM, Kristof Coucke wrote:
> Hi all,
>
> We have a Ceph cluster which has been expanded from 10 to 16
nodes.
> Each node has between 14 and 16 OSDs of which 2 are NVMe disks.
> Most disks (except NVMe's) are 16TB large.
>
> The expansion of 16 nodes went ok, but we've configured the
system to
> prevent auto balance towards the new disks (weight was set
to 0) so we
> could control the expansion.
>
> We started adding 6 disks last week (1 disk on each new
node) which didn't
> give a lot of issues.
> When the Ceph status indicated the PG degraded was almost
finished, we've
> added 2 disks on each node again.
>
> All seemed to go fine, till yesterday morning... IOs towards
the system
> were slowing down.
>
> Diving onto the nodes we could see that the OSD daemons are
consuming the
> CPU power, resulting in average CPU loads going near 10 (!).
>
> The RGWs nor monitors nor other involved servers are having
CPU issues
> (except for the management server which is fighting with
Prometheus), so
> it's latency seems to be related to the ODS hosts.
> All of the hosts are interconnected with 25Gbit connections,
no bottlenecks
> are reached on the network either.
>
> Important piece of information: We are using erasure coding
(6/3), and we
> do have a lot of small files...
> The current health detail indicates degraded health
redundancy where
> 1192911/103387889228 objects are degraded. (1 pg degraded, 1
pg undersized).
>
> Diving into the historic ops of an OSD we can see that the
main latency is
> found between the event "queued_for_pg" and "reached_pg".
(Averaging +/- 3
> secs)
>
> As the system load is quite high I assume the systems are busy
> recalculating the code chunks for using the new disks we've
added (though
> not sure), but I was wondering how I can better fine tune
the system or
> pinpoint the exact bottle neck.
> Latency towards the disks doesn't seem an issue at first
sight...
>
> We are running Ceph 14.2.11
>
> Who can give me some thoughts on how I can better pinpoint
the bottle neck?
>
> Thanks
>
> Kristof
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