Re: Adding OSD's results in slow ops, inactive PG's

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this sounds a bit like a customer issue we had almost two years ago. Basically, it was about mon_max_pg_per_osd (default 250) which was exceeded during the first activating OSD (and the last remaining stopping OSD). You can read all the details in the lengthy thread [1]. But if this is was the actual issue you probably should see something like this in the logs:

2022-04-06 14:24:55.256 7f8bb5a0e700 1 osd.8 43377 maybe_wait_for_max_pg withhold creation of pg 75.56s16: 750 >= 750

In our case we did the opposite and removed an entire host. I'll just quote Josh's explanation from the mentioned thread:

1. All OSDs on the host are purged per above.
2. New OSDs are created.
3. As they come up, one by one, CRUSH starts to assign PGs to them.
Importantly, when the first OSD comes up, it gets a large number of
OSDs, exceeding mon_max_pg_per_osd. Thus, some of these PGs don't
4. As each of the remaining OSDs come up, CRUSH re-assigns some PGs to them.
5. Finally, all OSDs are up. However, any PGs that were stuck in
"activating" from step 3 that were _not_ reassigned to other OSDs are
still stuck in "activating", and need a repeer or OSD down/up cycle to
restart peering for them. (At least in Pacific, tweaking
mon_max_pg_per_osd also allows some of these PGs to make peering

Note that during backfill/recovery the limit is 750 (mon_max_pg_per_osd * osd_max_pg_per_osd_hard_ratio ==> 250 * 3 = 750). As a workaround we increased osd_max_pg_per_osd_hard_ratio to 5 and the issue was never seen again.
Can you check the logs for that message?



Zitat von Ruben Vestergaard <rubenv@xxxxxxxx>:


We have a cluster with which currently looks like so:

      mon: 5 daemons, quorum lazy,jolly,happy,dopey,sleepy (age 13d)
mgr: jolly.tpgixt(active, since 25h), standbys: dopey.lxajvk, lazy.xuhetq
      mds: 1/1 daemons up, 2 standby
      osd: 449 osds: 425 up (since 15m), 425 in (since 5m); 5104 remapped pgs
      volumes: 1/1 healthy
      pools:   13 pools, 11153 pgs
      objects: 304.11M objects, 988 TiB
      usage:   1.6 PiB used, 1.4 PiB / 2.9 PiB avail
      pgs:     6/1617270006 objects degraded (0.000%)
               366696947/1617270006 objects misplaced (22.674%)
               6043 active+clean
               5041 active+remapped+backfill_wait
               66   active+remapped+backfilling
               2    active+recovery_wait+degraded+remapped
               1    active+recovering+degraded

It's currently rebalancing after adding a node, but this rebalance has been rather slow -- right now it's running 66 backfills, but it seems to stabilize around 8 backfills eventually. We figured that perhaps adding another node might speed things up.

Immediately upon adding the node, we get slow ops and inactive PG's. Removing the new node gets us back in working order.

It turns out that even adding 1 OSD breaks the cluster, and immediately sends it here:

[WRN] PG_DEGRADED: Degraded data redundancy: 6/1617265712 objects degraded (0.000%), 3 pgs degraded pg 37.c8 is active+recovery_wait+degraded+remapped, acting [410,163,236,209,7,283,155,143,78] pg 37.1a1 is active+recovering+degraded, acting [234,424,163,74,22,128,177,153,181] pg 37.1da is active+recovery_wait+degraded+remapped, acting [163,408,230,190,93,284,50,78,44] [WRN] SLOW_OPS: 22 slow ops, oldest one blocked for 54 sec, daemons [osd.11,osd.110,osd.112,osd.117,osd.120,osd.123,osd.13,osd.136,osd.144,osd.157]... have slow ops.

The OSD added had number 431, so it does not appear to be the immediate cause of the slow ops, however, removing 431 immediately clears the problem.

We thought we might be experiencing 'Crush giving up too soon' symptoms [1], as we have seen similar behaviour on another pool, but it does not appear to be the case here. We went through the motions described on the page and everything looked OK.

At least one pool which stops working is a 4+2 EC pool, placed on spinning rust, some 200-ish disks distributed across 13 nodes. I'm not sure if other pools break, but that particular 4+2 EC pool is rather important so I'm a little wary of experimenting blindly.

Any thoughts on where to look next?

Ruben Vestergaard

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