On 12/09/18 17:06, Ján Senko wrote:
We are benchmarking a test machine which has:
8 cores, 64GB RAM
12 * 12 TB HDD (SATA)
2 * 480 GB SSD (SATA)
1 * 240 GB SSD (NVME)
Ceph Mimic
Baseline benchmark for HDD only (Erasure Code 4+2)
Write 420 MB/s, 100 IOPS, 150ms latency
Read 1040 MB/s, 260 IOPS, 60ms latency
Now we moved WAL to the SSD (all 12 WALs on single SSD, default size
(512MB)):
Write 640 MB/s, 160 IOPS, 100ms latency
Read identical as above.
Nice boost we thought, so we moved WAL+DB to the SSD (Assigned 30GB
for DB)
All results are the same as above!
Q: This is suspicious, right? Why is the DB on SSD not helping with
our benchmark? We use *rados bench*
*
*
We tried putting WAL on the NVME, and again, the results are the same
as on SSD.
Same for WAL+DB on NVME
Again, the same speed. Any ideas why we don't gain speed by using
faster HW here?
Jan
--
Jan Senko, Skype janos-
Phone in Switzerland: +41 774 144 602
Phone in Czech Republic: +420 777 843 818
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Hi Jan,
putting 12 wals + db on the same SSD is probably too much. try 4-5 may
give better results.
the recommendation i have is to run a load monitoring tool
(atop/sar/collectl) while you are bench-marking and look for %
utilization for disks and cpus, this will let you know without guessing
where the bottleneck is : could be your ssd or maybe your cpu are saturated.
/Maged
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