30 Jan
2023
30 Jan
'23
12:40 a.m.
Looks like this is going to take a few days. I hope to manage the
available performance for VMs with osd_snap_trim_sleep_ssd.
I'm wondering if after that long snaptrim process you went through, was
your cluster was stable again and snapshots/snaptrims did work properly?
On 1/29/23 16:01, Matt Vandermeulen wrote:
I should have explicitly stated that during the
recovery, it was still
quite bumpy for customers. Some snaptrims were very quick, some took
what felt like a really long time. This was however a cluster with a
very large number of volumes and a long, long history of snapshots.
I'm not sure what the difference will be from our case versus a single
large volume with a big snapshot.
On 2023-01-28 20:45, Victor Rodriguez wrote:
--
On 1/29/23 00:50, Matt Vandermeulen wrote:
I've observed a similar horror when upgrading
a cluster from
Luminous to Nautilus, which had the same effect of an overwhelming
amount of snaptrim making the cluster unusable.
In our case, we held its hand by setting all OSDs to have zero max
trimming PGs, unsetting nosnaptrim, and then slowly enabling
snaptrim a few OSDs at a time. It was painful to babysit but it
allowed the cluster to catch up without falling over.
That's an interesting approach! Thanks!
On preliminary tests seems that just running snaptrim on a single PG
of a single OSD still makes the cluster barely usable. I have to
increase osd_snap_trim_sleep_ssd to ~1 so the cluster remains usable
by getting a third of its performance. After a while, a few PG got
trimmed and feels like some of them are harder to trim than others,
as some need a higher osd_snap_trim_sleep_ssd value to let the
cluster perform.
I don't know how long this is going to take... Maybe recreating the
OSD's and dealing with the rebalance is a better option?
There's something ugly going on here... I would really like to put my
finger on it.
On 2023-01-28 19:43, Victor Rodriguez wrote:
> After some investigation this is what I'm seeing:
>
> - OSD processes get stuck at least at 100% CPU if I ceph osd unset
> nosnaptrim. They keep at 100% CPU even if I ceph osd set
> nosnaptrim. They stayed like that for at least 26 hours. Some quick
> benchmarks don't show a reduction of the performance of the cluster.
>
> - Restarting a OSD lowers it's CPU usage to typical levels, as
> expected, but it also usually sets some other OSD in a different
> host to typical levels.
>
> - All OSDs in this cluster take quite a bit to start: between 35 to
> 70 seconds depending on the OSD. Clearly much longer than any other
> OSD in any of my clusters.
>
> - I believe that the size of the rocksdb database is dumped in the
> OSD log when an automatic compact operation is triggered. The "sum"
> sizes of these OSD range between 2.5 and 5.1 GB. Thats way bigger
> that those in any other cluster I have.
>
> - ceph daemon osd.* calc_objectstore_db_histogram is giving values
> for num_pgmeta_omap (I don't know what it is) way bigger than those
> on any other of my clusters for some OSD. Also, values are not
> similar among the OSD which hold the same PGs.
>
> osd.0: "num_pgmeta_omap": 17526766,
> osd.1: "num_pgmeta_omap": 2653379,
> osd.2: "num_pgmeta_omap": 12358703,
> osd.3: "num_pgmeta_omap": 6404975,
> osd.6: "num_pgmeta_omap": 19845318,
> osd.7: "num_pgmeta_omap": 6043083,
> osd.12: "num_pgmeta_omap": 18666776,
> osd.13: "num_pgmeta_omap": 615846,
> osd.14: "num_pgmeta_omap": 13190188,
>
> - Compacting the OSD barely reduces rocksdb size and does not
> reduce num_pgmeta_omap at all.
>
> - This is the only cluster I have were there are some RBD images
> that I mount directly from some clients, that is, they are not
> disks for QEMU/Proxmox VMs. Maybe I have something misconfigured
> related to this? This cluster is at least two and half years old
> an never had this issue with snaptrims.
>
> Thanks in advance!
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