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 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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