Performance issues with deep-scrub since upgrading from v12.2.2 to v12.2.5

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Hello,

We recently upgraded Ceph from version 12.2.2 to version 12.2.5. Since the upgrade we've been having performance issues which seem to relate to when deep-scrub actions are performed.

Most of the time deep-scrub actions only takes a couple of seconds at most, however ocassionaly it takes 10 minutes. It's either a few seconds or 10 minutes, never a couple of minutes or anything else in between. This has been happening since the upgrade.

For example see the following:

2018-06-14 10:11:46.337086 7fbd3528b700  0 log_channel(cluster) log [DBG] : 15.2dc deep-scrub starts
2018-06-14 10:11:50.947843 7fbd3528b700  0 log_channel(cluster) log [DBG] : 15.2dc deep-scrub ok

2018-06-14 10:45:49.575042 7fbd32a86700  0 log_channel(cluster) log [DBG] : 14.1 deep-scrub starts
2018-06-14 10:55:53.326309 7fbd32a86700  0 log_channel(cluster) log [DBG] : 14.1 deep-scrub ok

2018-06-14 10:58:28.652360 7fbd33a88700  0 log_channel(cluster) log [DBG] : 15.5f deep-scrub starts
2018-06-14 10:58:33.411769 7fbd2fa80700  0 log_channel(cluster) log [DBG] : 15.5f deep-scrub ok

The scrub on PG 14.1 took pretty much exactly 10 minutes, the others only about 5 seconds. It matches the value of "osd scrub finalize thread timeout" which is currently set to 10 minutes, however I'm not sure if it's related or just a coincidence. It's not just this PG, but there's a bunch of them, also on difference nodes and OSD's.

PG dump for this problematic PG is as follows:

PG_STAT OBJECTS MISSING_ON_PRIMARY DEGRADED MISPLACED UNFOUND BYTES      LOG  DISK_LOG STATE        STATE_STAMP                VERSION       REPORTED       UP         UP_PRIMARY ACTING     ACTING_PRIMARY LAST_SCRUB    SCRUB_STAMP                LAST_DEEP_SCRUB DEEP_SCRUB_STAMP           SNAPTRIMQ_LEN
14.1      10573                  0        0         0       0          0 1579     1579 active+clean 2018-06-14 15:47:32.832222  1215'1291261   1215:7062174   [3,8,20]          3   [3,8,20]              3  1179'1288697 2018-06-14 10:55:53.326320    1179'1288697 2018-06-14 10:55:53.326320             0

During the longer running deep-scrub actions we're also running into performance problems.

Any idea what's going wrong?

Thanks

Sander
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