Hi,
It is very useful to "set up expectations" from a performance perspective
I have a cluster using 3 DELL R620 with 64 GB RAM and
10 GB cluster network
I've seen numerous posts and articles about the topic mentioning the following formula
( for disks WAL/DB on it )
OSD / replication / 2
Example
My HDD are capable of 150 MB/s
If I have 6 OSDs, expected throughput should be aroung 250 MB/s for a pool withe replication =2
( 150 x 6 / 2 / 2 )
How would one asses the impact of using SSD for WAL/DB i.e what performance gains should I expect ?
Example:
adding an 500MB/s SDD for every 2 HDD
adding an 500MB/s SDD for every 2 HDD
Should I expect that kind of throuput on the client ( e.g Windows VM running on datastore create on RBD image shared via iSCSI ) ?
The reason I am asking is that despite rados bench meeting the expectaion, local performance test are 4 times worse
rados bench -p rbd 120 write --no-cleanup && rados bench -p rbd 120 seq
Total time run: 120.813979
Total writes made: 6182
Write size: 4194304
Object size: 4194304
Bandwidth (MB/sec): 204.678
Stddev Bandwidth: 36.2292
Max bandwidth (MB/sec): 280
Min bandwidth (MB/sec): 44
Average IOPS: 51
Stddev IOPS: 9
Max IOPS: 70
Min IOPS: 11
Average Latency(s): 0.312613
Stddev Latency(s): 0.524001
Max latency(s): 2.61579
Min latency(s): 0.0113714
Total time run: 113.850422
Total reads made: 6182
Read size: 4194304
Object size: 4194304
Bandwidth (MB/sec): 217.197
Average IOPS: 54
Stddev IOPS: 7
Max IOPS: 80
Min IOPS: 31
Average Latency(s): 0.293956
Max latency(s): 1.99958
Min latency(s): 0.0192862
Local test using CrystalDiskMark
57 MB/s seq read
43 MB/s seq write
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