After my last round of backfills completed, I started 5 more bluestore conversions, which helped me recognize a very specific pattern of performance.
pool objects-ssd id 20 recovery io 757 MB/s, 10845 objects/s
pool fs-metadata-ssd id 16 recovery io 0 B/s, 36265 keys/s, 1633 objects/s client io 2544 kB/s rd, 36788 B/s wr, 1 op/s rd, 0 op/s wr
The “non-throttled” backfills are only coming from filestore SSD OSD’s. When backfilling from bluestore SSD OSD’s, they appear to be throttled at the aforementioned <20 ops per OSD.
This would corroborate why the first batch of SSD’s I migrated to bluestore were all at “full” speed, as all of the OSD’s they were backfilling from were filestore based, compared to increasingly bluestore backfill targets, leading to increasingly long backfill times as I move from one host to the next.
Looking at the recovery settings, the recovery_sleep and recovery_sleep_ssd values across bluestore or filestore OSDs are showing as 0 values, which means no sleep/throttle if I am reading everything correctly.
sudo ceph daemon osd.73 config show | grep recovery "osd_allow_recovery_below_min_size": "true", "osd_debug_skip_full_check_in_recovery": "false", "osd_force_recovery_pg_log_entries_factor": "1.300000", "osd_min_recovery_priority": "0", "osd_recovery_cost": "20971520", "osd_recovery_delay_start": "0.000000", "osd_recovery_forget_lost_objects": "false", "osd_recovery_max_active": "35", "osd_recovery_max_chunk": "8388608", "osd_recovery_max_omap_entries_per_chunk": "64000", "osd_recovery_max_single_start": "1", "osd_recovery_op_priority": "3", "osd_recovery_op_warn_multiple": "16", "osd_recovery_priority": "5", "osd_recovery_retry_interval": "30.000000", "osd_recovery_sleep": "0.000000", "osd_recovery_sleep_hdd": "0.100000", "osd_recovery_sleep_hybrid": "0.025000", "osd_recovery_sleep_ssd": "0.000000", "osd_recovery_thread_suicide_timeout": "300", "osd_recovery_thread_timeout": "30", "osd_scrub_during_recovery": "false",
As far as I know, the device class is configured correctly as far as I know, it all shows as ssd/hdd correctly in ceph osd tree.
So hopefully this may be enough of a smoking gun to help narrow down where this may be stemming from.
Thanks,
Reed
Here is a [1] link to a ML thread tracking some slow backfilling on bluestore. It came down to the backfill sleep setting for them. Maybe it will help.
Probably unrelated, but I do keep seeing this odd negative objects degraded message on the fs-metadata pool:
pool fs-metadata-ssd id 16 -34/3 objects degraded (-1133.333%) recovery io 0 B/s, 89 keys/s, 2 objects/s client io 51289 B/s rd, 101 kB/s wr, 0 op/s rd, 0 op/s wr
Don’t mean to clutter the ML/thread, however it did seem odd, maybe its a culprit? Maybe its some weird sampling interval issue thats been solved in 12.2.3?
Thanks,
Reed
Below is ceph -s cluster: id: {id} health: HEALTH_WARN noout flag(s) set 260610/1068004947 objects misplaced (0.024%) Degraded data redundancy: 23157232/1068004947 objects degraded (2.168%), 332 pgs unclean, 328 pgs degraded, 328 pgs undersized
services: mon: 3 daemons, quorum mon02,mon01,mon03 mgr: mon03(active), standbys: mon02 mds: cephfs-1/1/1 up {0=mon03=up:active}, 1 up:standby osd: 74 osds: 74 up, 74 in; 332 remapped pgs flags noout
data: pools: 5 pools, 5316 pgs objects: 339M objects, 46627 GB usage: 154 TB used, 108 TB / 262 TB avail pgs: 23157232/1068004947 objects degraded (2.168%) 260610/1068004947 objects misplaced (0.024%) 4984 active+clean 183 active+undersized+degraded+remapped+backfilling 145 active+undersized+degraded+remapped+backfill_wait 3 active+remapped+backfill_wait 1 active+remapped+backfilling
io: client: 8428 kB/s rd, 47905 B/s wr, 130 op/s rd, 0 op/s wr recovery: 37057 kB/s, 50 keys/s, 217 objects/s
Also the two pools on the SSDs, are the objects pool at 4096 PG, and the fs-metadata pool at 32 PG.
Are you sure the recovery is actually going slower, or are the individual ops larger or more expensive?
The objects should not vary wildly in size. Even if they were differing in size, the SSDs are roughly idle in their current state of backfilling when examining wait in iotop, or atop, or sysstat/iostat.
This compares to when I was fully saturating the SATA backplane with over 1000MB/s of writes to multiple disks when the backfills were going “full speed.”
Here is a breakdown of recovery io by pool:
pool objects-ssd id 20 recovery io 6779 kB/s, 92 objects/s client io 3071 kB/s rd, 50 op/s rd, 0 op/s wr
pool fs-metadata-ssd id 16 recovery io 0 B/s, 28 keys/s, 2 objects/s client io 109 kB/s rd, 67455 B/s wr, 1 op/s rd, 0 op/s wr
pool cephfs-hdd id 17 recovery io 40542 kB/s, 158 objects/s client io 10056 kB/s rd, 142 op/s rd, 0 op/s wr
So the 24 HDD’s are outperforming the 50 SSD’s for recovery and client traffic at the moment, which seems conspicuous to me.
Most of the OSD’s with recovery ops to the SSDs are reporting 8-12 ops, with one OSD occasionally spiking up to 300-500 for a few minutes. Stats being pulled by both local CollectD instances on each node, as well as the Influx plugin in MGR as we evaluate that against collectd.
Thanks,
Reed
What's the output of "ceph -s" while this is happening?
Is there some identifiable difference between these two states, like you get a lot of throughput on the data pools but then metadata recovery is slower?
Are you sure the recovery is actually going slower, or are the individual ops larger or more expensive?
My WAG is that recovering the metadata pool, composed mostly of directories stored in omap objects, is going much slower for some reason. You can adjust the cost of those individual ops some by changing osd_recovery_max_omap_entries_per_chunk (default: 8096), but I'm not sure which way you want to go or indeed if this has anything to do with the problem you're seeing. (eg, it could be that reading out the omaps is expensive, so you can get higher recovery op numbers by turning down the number of entries per request, but not actually see faster backfilling because you have to issue more requests.) -Greg Hi all,
I am running into an odd situation that I cannot easily explain. I am currently in the midst of destroy and rebuild of OSDs from filestore to bluestore. With my HDDs, I am seeing expected behavior, but with my SSDs I am seeing unexpected behavior. The HDDs and SSDs are set in crush accordingly.
My path to replacing the OSDs is to set the noout, norecover, norebalance flag, destroy the OSD, create the OSD back, (iterate n times, all within a single failure domain), unset the flags, and let it go. It finishes, rinse, repeat.
For the SSD OSDs, they are SATA SSDs (Samsung SM863a) , 10 to a node, with 2 NVMe drives (Intel P3700), 5 SATA SSDs to 1 NVMe drive, 16G partitions for block.db (previously filestore journals). 2x10GbE networking between the nodes. SATA backplane caps out at around 10 Gb/s as its 2x 6 Gb/s controllers. Luminous 12.2.2.
When the flags are unset, recovery starts and I see a very large rush of traffic, however, after the first machine completed, the performance tapered off at a rapid pace and trickles. Comparatively, I’m getting 100-200 recovery ops on 3 HDDs, backfilling from 21 other HDDs, where as I’m getting 150-250 recovery ops on 5 SSDs, backfilling from 40 other SSDs. Every once in a while I will see a spike up to 500, 1000, or even 2000 ops on the SSDs, often a few hundred recovery ops from one OSD, and 8-15 ops from the others that are backfilling.
This is a far cry from the more than 15-30k recovery ops that it started off recovering with 1-3k recovery ops from a single OSD to the backfilling OSD(s). And an even farther cry from the >15k recovery ops I was sustaining for over an hour or more before. I was able to rebuild a 1.9T SSD (1.1T used) in a little under an hour, and I could do about 5 at a time and still keep it at roughly an hour to backfill all of them, but then I hit a roadblock after the first machine, when I tried to do 10 at a time (single machine). I am now still experiencing the same thing on the third node, while doing 5 OSDs at a time.
The pools associated with these SSDs are cephfs-metadata, as well as a pure rados object pool we use for our own internal applications. Both are size=3, min_size=2.
Recovery parameters for the OSDs match what was in the previous thread, sans the osd conf block listed. And current osd_max_backfills = 30 and osd_recovery_max_active = 35. Very little activity on the OSDs during this period, so should not be any contention for iops on the SSDs.
The only oddity that I can attribute to things is that we had a few periods of time where the disk load on one of the mons was high enough to cause the mon to drop out of quorum for a brief amount of time, a few times. But I wouldn’t think backfills would just get throttled due to mons flapping.
Hopefully someone has some experience or can steer me in a path to improve the performance of the backfills so that I’m not stuck in backfill purgatory longer than I need to be.
Linking an imgur album with some screen grabs of the recovery ops over time for the first machine, versus the second and third machines to demonstrate the delta between them.
Also including a ceph osd df of the SSDs, highlighted in red are the OSDs currently backfilling. Could this possibly be PG overdose? I don’t ever run into ‘stuck activating’ PGs, its just painfully slow backfills, like they are being throttled by ceph, that are causing me to worry. Drives aren’t worn, <30 P/E cycles on the drives, so plenty of life left in them.
Thanks, Reed
$ ceph osd df ID CLASS WEIGHT REWEIGHT SIZE USE AVAIL %USE VAR PGS 24 ssd 1.76109 1.00000 1803G 1094G 708G 60.69 1.08 260 25 ssd 1.76109 1.00000 1803G 1136G 667G 63.01 1.12 271 26 ssd 1.76109 1.00000 1803G 1018G 785G 56.46 1.01 243 27 ssd 1.76109 1.00000 1803G 1065G 737G 59.10 1.05 253 28 ssd 1.76109 1.00000 1803G 1026G 776G 56.94 1.02 245 29 ssd 1.76109 1.00000 1803G 1132G 671G 62.79 1.12 270 30 ssd 1.76109 1.00000 1803G 944G 859G 52.35 0.93 224 31 ssd 1.76109 1.00000 1803G 1061G 742G 58.85 1.05 252 32 ssd 1.76109 1.00000 1803G 1003G 799G 55.67 0.99 239 33 ssd 1.76109 1.00000 1803G 1049G 753G 58.20 1.04 250 34 ssd 1.76109 1.00000 1803G 1086G 717G 60.23 1.07 257 35 ssd 1.76109 1.00000 1803G 978G 824G 54.26 0.97 232 36 ssd 1.76109 1.00000 1803G 1057G 745G 58.64 1.05 252 37 ssd 1.76109 1.00000 1803G 1025G 777G 56.88 1.01 244 38 ssd 1.76109 1.00000 1803G 1047G 756G 58.06 1.04 250 39 ssd 1.76109 1.00000 1803G 1031G 771G 57.20 1.02 246 40 ssd 1.76109 1.00000 1803G 1029G 774G 57.07 1.02 245 41 ssd 1.76109 1.00000 1803G 1033G 770G 57.28 1.02 245 42 ssd 1.76109 1.00000 1803G 993G 809G 55.10 0.98 236 43 ssd 1.76109 1.00000 1803G 1072G 731G 59.45 1.06 256 44 ssd 1.76109 1.00000 1803G 1039G 763G 57.64 1.03 248 45 ssd 1.76109 1.00000 1803G 992G 810G 55.06 0.98 236 46 ssd 1.76109 1.00000 1803G 1068G 735G 59.23 1.06 254 47 ssd 1.76109 1.00000 1803G 1020G 783G 56.57 1.01 242 48 ssd 1.76109 1.00000 1803G 945G 857G 52.44 0.94 225 49 ssd 1.76109 1.00000 1803G 649G 1154G 36.01 0.64 139 50 ssd 1.76109 1.00000 1803G 426G 1377G 23.64 0.42 83 51 ssd 1.76109 1.00000 1803G 610G 1193G 33.84 0.60 131 52 ssd 1.76109 1.00000 1803G 558G 1244G 30.98 0.55 118 53 ssd 1.76109 1.00000 1803G 731G 1072G 40.54 0.72 161 54 ssd 1.74599 1.00000 1787G 859G 928G 48.06 0.86 229 55 ssd 1.74599 1.00000 1787G 942G 844G 52.74 0.94 252 56 ssd 1.74599 1.00000 1787G 928G 859G 51.94 0.93 246 57 ssd 1.74599 1.00000 1787G 1039G 748G 58.15 1.04 277 58 ssd 1.74599 1.00000 1787G 963G 824G 53.87 0.96 255 59 ssd 1.74599 1.00000 1787G 909G 877G 50.89 0.91 241 60 ssd 1.74599 1.00000 1787G 1039G 748G 58.15 1.04 277 61 ssd 1.74599 1.00000 1787G 892G 895G 49.91 0.89 238 62 ssd 1.74599 1.00000 1787G 927G 859G 51.90 0.93 245 63 ssd 1.74599 1.00000 1787G 864G 922G 48.39 0.86 229 64 ssd 1.74599 1.00000 1787G 968G 819G 54.16 0.97 257 65 ssd 1.74599 1.00000 1787G 892G 894G 49.93 0.89 237 66 ssd 1.74599 1.00000 1787G 951G 836G 53.23 0.95 252 67 ssd 1.74599 1.00000 1787G 878G 908G 49.16 0.88 232 68 ssd 1.74599 1.00000 1787G 899G 888G 50.29 0.90 238 69 ssd 1.74599 1.00000 1787G 948G 839G 53.04 0.95 252 70 ssd 1.74599 1.00000 1787G 914G 873G 51.15 0.91 246 71 ssd 1.74599 1.00000 1787G 1004G 782G 56.21 1.00 266 72 ssd 1.74599 1.00000 1787G 812G 974G 45.47 0.81 216 73 ssd 1.74599 1.00000 1787G 932G 855G 52.15 0.93 247
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