With good hardware and correct configuration, an all flash cluster should give: approx 1-2K write iops per thread (0.5-1 ms latency) approx 2-5K read iops per thread (0.2-0.5 ms latency) This is dependent on quality of drives and cpu/frequency but independent on number of drives or cores. Total iops should scale as you add threads, linearly at first but the rate will slowly saturate based on number of drives and cores. With 8 threads, you should easily get 8k write, 16k read iops or more. With only 8 threads/queue depth, you would not need more than 3 drives in total for performance, any extra drives will be for capacity as they will be idle most of the time. Some things to consider to get decent speeds: 1) Make sure you use enterprise ssd/nvme drives. Ceph syncs its writes, it is worth testing raw drive write speed using fio with direct,sync flags. 10K write iops and more is good. 2) tune your cpu: disable wait states, set min frequency: 100%, set governor to performance. Make sure you disable anything in BIOS relating to energy savings :) 3) disable volatile cache on your nvme 4) set the i/o scheduler on nvme drives to "none" 5) lower read_ahead_kb to 64KB or lower so not to affect random reads. 6) There are advanced tuning like numa pinning, but you should get decent speeds without doing fancy stuff. I would not recommend any drive caching. This could be good for bursty workloads but typically give worse results for consistent heavy loads. Ceph is best for consistent high load, if all you need is a single MySQL db with a few threads that may at times have bursty load but is mostly quiet, then probably Ceph is not the best solution. If however you have this MySQL db in one of your vms among thousands of other vms, then Ceph will be ideal. /Maged On 07/06/2024 18:32, Mark Lehrer wrote:
I've been using MySQL on Ceph forever, and have been down this road before but it's been a couple of years so I wanted to see if there is anything new here.
So the TL:DR version of this email - is there a good way to improve 16K write IOPs with a small number of threads? The OSDs themselves are idle so is this just a weakness in the algorithms or do ceph clients need some profiling? Or "other"?
Basically, this is one of the worst possible Ceph workloads so it is fun to try to push the limits. I also happen have a MySQL instance that is reaching the write IOPs limit so this is also a last-ditch effort to keep it on Ceph.
This cluster is as straightforward as it gets... 6 servers with 10 SSDs each, 100 Gb networking. I'm using size=3. During operations, the OSDs are more or less idle so I don't suspect any hardware limitations.
MySQL has no parallelism so the number of threads and effective queue depth stay pretty low. Therefore, as a proxy for MySQL I use rados bench with 16K writes and 8 threads. The RBD actually gets about 2x this level - still not so great.
I get about 2000 IOPs with this test:
# rados bench -p volumes 10 write -t 8 -b 16K hints = 1 Maintaining 8 concurrent writes of 16384 bytes to objects of size 16384 for up to 10 seconds or 0 objects Object prefix: benchmark_data_fstosinfra-5_3652583 sec Cur ops started finished avg MB/s cur MB/s last lat(s) avg lat(s) 0 0 0 0 0 0 - 0 1 8 2050 2042 31.9004 31.9062 0.00247633 0.00390848 2 8 4306 4298 33.5728 35.25 0.00278488 0.00371784 3 8 6607 6599 34.3645 35.9531 0.00277546 0.00363139 4 7 8951 8944 34.9323 36.6406 0.00414908 0.00357249 5 8 11292 11284 35.257 36.5625 0.00291434 0.00353997 6 8 13588 13580 35.3588 35.875 0.00306094 0.00353084 7 7 15933 15926 35.5432 36.6562 0.00308388 0.0035123 8 8 18361 18353 35.8399 37.9219 0.00314996 0.00348327 9 8 20629 20621 35.7947 35.4375 0.00352998 0.0034877 10 5 23010 23005 35.9397 37.25 0.00395566 0.00347376 Total time run: 10.003 Total writes made: 23010 Write size: 16384 Object size: 16384 Bandwidth (MB/sec): 35.9423 Stddev Bandwidth: 1.63433 Max bandwidth (MB/sec): 37.9219 Min bandwidth (MB/sec): 31.9062 Average IOPS: 2300 Stddev IOPS: 104.597 Max IOPS: 2427 Min IOPS: 2042 Average Latency(s): 0.0034737 Stddev Latency(s): 0.00163661 Max latency(s): 0.115932 Min latency(s): 0.00179735 Cleaning up (deleting benchmark objects) Removed 23010 objects Clean up completed and total clean up time :7.44664
Are there any good options to improve this? It seems like the client side is the bottleneck since the OSD servers are at like 15% utilization.
Thanks, Mark _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-leave@ceph.io