rep3datapool pg num is 512, Average number of PG replicas per OSD is 139 scrubs, balancer and pg autoscaler was disabled RAM is 128G, swap is 0 From: Anthony D'Atri Date: 2024-10-30 12:03 To: Louisa CC: ceph-users Subject: Re: [ceph-users] why performance difference between 'rados bench seq' and 'rados bench rand' quite significant The good Mr. Nelson and others may have more to contribute, but a few thoughts: * Running for 60 or 120 seconds isn’t quantitative: rados bench typically exhibits a clear ramp-up; watch the per-second stats. * Suggest running for 10 minutes, three times in a row and averaging the results * How many PGs in rep3datapool? Average number of PG replicas per OSD shown by `ceph osd df` ? I would shoot for 150 - 200 in your case. * Disable scrubs, the balancer, and the pg autoscaler during benching. * If you have OS swap configured, disable it and reboot. How much RAM?
On Oct 29, 2024, at 11:43 PM, Louisa <lushasha08@126.com> wrote:
Hi all, We used 'rados bench' to test 4k object read and write operations. Our cluster is pacific, one node, 11 bluestore osd ,db and wal share the block device. Block device is HDD.
1. testing 4k write with command 'rados bench 120 write -t 16 -b 4K -p rep3datapool --run-name 4kreadwrite --no-cleanup'
2. Before tesing 4k reads, we restarted all OSD daemons. The perfomance of 'rados bench 120 seq -t 16 -p rep3datapool --run-name 4kreadwrite' was very good, which Average IOPS: 17735; using 'ceph daemon osd.1 perf dump rocksdb' , we found the rocksdb:get_latency avgcount: 15189, avgtime: 0.000012947 (12.9us)
3. Before tesing 4k rand reads, we restarted all OSD daemons. 'rados bench 60 rand -t 16 -p rep3datapool --run-name 4kreadwrite' average IOPS: 2071 rocksdb:get_latency avgcount: 8756, avgtime: 0.001761293 (1.7ms)
Q1: Why performance difference between 'rados bench seq' and 'rados bench rand' quite significant? How to explain the rocksdb get_latency perfomance between this two scenario?
4. We write 40w 4k object to the pool, restarted all OSD daemons. running 'rados bench 120 seq -t 16 -p rep3datapool --run-name 4kreadwrite' again. Average IOPS~= 2000. rocsdb:get_latency avgtime also reached milliseconds level Q2: Why 'rados bench seq' performance decresing extremly after writing some more 4k object to the pool?
Q3: Is there any methods and suggestions to optimized the read performance of this scenario under this hardware configuration.
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