I will definitely follow your steps and apply bluefs_buffered_io=true via ceph.conf and restart. My first try was to update these dynamically. I’ll report when it’s done. We monitor our clusters via Telegraf (Ceph input Plugin) and InfluxDB and a custom Grafana dashboard fitted for our needs. Björn
Am 13.02.2021 um 09:23 schrieb Frank Schilder <frans@dtu.dk>:
Ahh, OK. I'm not sure if it has that effect. What people observed was, that rocks-DB access became faster due to system buffer cache hits. This has an indirect influence on data access latency.
The typical case is "high IOPs on WAL/DB device after upgrade" and setting bluefs_buffered_io=true got this back to normal also improving client performance as a result.
Your latency graphs look actually suspiciously like it should work for you. Are you sure the OSD is using the value? I had problems with setting some parameters, I needed to include them in the ceph.conf file and restart to force them through.
A sign that bluefs_buffered_io=true is applied is rapidly increasing system buffer usage reported by top or free. If the values reported are similar for all hosts, bluefs_buffered_io is still disabled.
If I may ask, what framework are you using to pull these graphs? Is there a graphana dashboard one can download somewhere or is it something you implemented yourself? I plan to enable prometheus on our cluster, but don't know about a good data sink providing a pre-defined dashboard.
Best regards, ================= Frank Schilder AIT Risø Campus Bygning 109, rum S14
________________________________________ From: Björn Dolkemeier <b.dolkemeier@dbap.de> Sent: 13 February 2021 08:51:11 To: Frank Schilder Cc: ceph-users@ceph.io Subject: Re: [ceph-users] Latency increase after upgrade 14.2.8 to 14.2.16
Thanks for the quick reply, Frank.
Sorry, the graphs/attachment where filtered. Here is an example of one latency: https://drive.google.com/file/d/1qSWmSmZ6JXVweepcoY13ofhfWXrBi2uZ/view?usp=s...
I’m aware that the overall performance depends on the slowest OSD.
What I expect is that bluefs_buffered_io=true set on one OSD reflects in dropped latencies for that particular OSD.
Best regards, Björn
Am 13.02.2021 um 07:39 schrieb Frank Schilder <frans@dtu.dk<mailto:frans@dtu.dk>>:
The graphs were forgotten or filtered out.
Changing the buffered_io value on one host will not change client IO performance as its always the slowest OSD thats decisive. However, it should have an effect on the IOP/s load reported by iostat on the disks on the host.
Does setting bluefs_buffered_io=true on all hosts have an effect on client IO? Note that it might need a restart even if the documentation says otherwise.
Best regards, ================= Frank Schilder AIT Risø Campus Bygning 109, rum S14
________________________________________ From: Björn Dolkemeier <b.dolkemeier@dbap.de<mailto:b.dolkemeier@dbap.de>> Sent: 13 February 2021 07:16:06 To: ceph-users@ceph.io<mailto:ceph-users@ceph.io> Subject: [ceph-users] Latency increase after upgrade 14.2.8 to 14.2.16
Hi,
after upgrading Ceph from 14.2.8 to 14.2.16 we experienced increased latencies. There were no changes in hardware, configuration, workload or networking, just a rolling-update via ceph-ansible on running production cluster. The cluster consists of 16 OSDs (all SSD) over 4 Nodes. The VMs served via RBD from this cluster currently suffer on i/o wait cpu.
These are some latencies that are increased after the update: - op_r_latency - op_w_latency - kv_final_lat - state_kv_commiting_lat - submit_lat - subop_w_latency
Do these latencies point to KV/RocksDB?
These are some latencies which are NOT increased after the update: - kv_sync_lat - kv_flush_lat - kv_commit_lat
I attached one graph showing the massive increase after the update.
I tried setting bluefs_buffered_io=true (as it’s default value was changed and it was mentioned as performance relevant) for all OSDs in one host but this does not make a difference.
The ceph.conf is fairly simple:
[global] cluster network = xxx fsid = xxx mon host = xxx public network = xxx
[osd] osd memory target = 10141014425
Any ideas what to try? Help appreciated.
Björn
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