Re: Extremely high OSD memory utilization on Kraken 11.2.0 (with XFS -or- bluestore)

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Peter,

There are 624 PGs across 4 pools:

pool 0 'rbd' replicated size 3 min_size 2 crush_ruleset 0 object_hash rjenkins pg_num 64 pgp_num 64 last_change 2505 flags hashpspool stripe_width 0
        removed_snaps [1~3]
pool 3 'fsdata' erasure size 14 min_size 11 crush_ruleset 3 object_hash rjenkins pg_num 512 pgp_num 512 last_change 154 lfor 153 flags hashpspool crash_replay_interval 45 tiers 5 read_tier 5 write_tier 5 stripe_width 4160
pool 4 'fsmeta' replicated size 4 min_size 3 crush_ruleset 0 object_hash rjenkins pg_num 16 pgp_num 16 last_change 144 flags hashpspool stripe_width 0
pool 5 'fscache' replicated size 3 min_size 2 crush_ruleset 4 object_hash rjenkins pg_num 32 pgp_num 32 last_change 1016 flags hashpspool,incomplete_clones tier_of 3 cache_mode writeback target_bytes 100000000000 hit_set bloom{false_positive_probability: 0.05, target_size: 0, seed: 0} 86400s x4 decay_rate 0 search_last_n 0 stripe_width 0


Here's the ceph.conf. We're back to no extra configuration for bluestore caching, but previously we had attempted setting the directive bluestore_cache_size as low as 1073741.

[global]
        fsid                                                    = c4b3b4ec-fbc2-4861-913f-295ff64f70ad
        auth client required                                    = cephx
        auth cluster required                                   = cephx
        auth service required                                   = cephx

        cephx require signatures                                = true

        public network                                          = 10.42.0.0/16
        cluster network                                         = 10.43.100.0/24

        mon_initial_members                                     = benjamin, jake, jennifer
        mon_host                                                = 10.42.5.38,10.42.5.37,10.42.5.36

[osd]
        osd crush update on start                               = false


Thanks,
-Aaron

On Sat, Apr 15, 2017 at 5:39 AM, Peter Maloney <peter.maloney@xxxxxxxxxxxxxxxxxxxx> wrote:
How many PGs do you have? And did you change any config, like mds cache size? Show your ceph.conf.


On 04/15/17 07:34, Aaron Ten Clay wrote:
Hi all,

Our cluster is experiencing a very odd issue and I'm hoping for some guidance on troubleshooting steps and/or suggestions to mitigate the issue. tl;dr: Individual ceph-osd processes try to allocate > 90GiB of RAM and are eventually nuked by oom_killer.

I'll try to explain the situation in detail:

We have 24-4TB bluestore HDD OSDs, and 4-600GB SSD OSDs. The SSD OSDs are in a different CRUSH "root", used as a cache tier for the main storage pools, which are erasure coded and used for cephfs. The OSDs are spread across two identical machines with 128GiB of RAM each, and there are three monitor nodes on different hardware.

Several times we've encountered crippling bugs with previous Ceph releases when we were on RC or betas, or using non-recommended configurations, so in January we abandoned all previous Ceph usage, deployed LTS Ubuntu 16.04, and went with stable Kraken 11.2.0 with the configuration mentioned above. Everything was fine until the end of March, when one day we find all but a couple of OSDs are "down" inexplicably. Investigation reveals oom_killer came along and nuked almost all the ceph-osd processes.

We've gone through a bunch of iterations of restarting the OSDs, trying to bring them up one at a time gradually, all at once, various configuration settings to reduce cache size as suggested in this ticket: http://tracker.ceph.com/issues/18924...

I don't know if that ticket really pertains to our situation or not, I have no experience with memory allocation debugging. I'd be willing to try if someone can point me to a guide or walk me through the process.

I've even tried, just to see if the situation was  transitory, adding over 300GiB of swap to both OSD machines. The OSD procs managed to allocate, in a matter of 5-10 minutes, more than 300GiB of RAM pressure and became oom_killer victims once again.

No software or hardware changes took place around the time this problem started, and no significant data changes occurred either. We added about 40GiB of ~1GiB files a week or so before the problem started and that's the last time data was written.

I can only assume we've found another crippling bug of some kind, this level of memory usage is entirely unprecedented. What can we do?

Thanks in advance for any suggestions.
-Aaron


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--
Aaron Ten Clay
https://aarontc.com
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