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High storage latency on ESXi host (alien.top)

submitted 1 year ago by bonaventura84@alien.top to c/homelab@selfhosted.forum

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I've been going back and forth with this issue for some time but honestly I have no idea if the vCenter telemetry is something to rely on. I'm experiencing rather high latency on the storage on my VMs, most of them idle, only vCenter and virtual firewall generate some IOPS, 5 are shut down, other 3 VMs are linux machines that idle for 99%, even though they can spike 100ms per IO. Today I have decided to migrate a VM storage to another server to find that higher disk utilization reduces the latency on the host, how that makes any sense? I'm using P420 in RAID 10 with 4x4TB 7k SAS HDDs.

Host latency:

https://preview.redd.it/cqvmy550ty1c1.png?width=986&format=png&auto=webp&s=f5823391eb6cd82cb9612b44aa2768087bf619e1

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[–] Roland_Bodel_the_2nd@alien.top 1 points 1 year ago (4 children)

15-30ms latency seems reasonable for that hardware (P420 in RAID 10 with 4x4TB 7k SAS HDDs.)

Basically your single SAS disk can do ~150IOPS random, so worst case of 4k random reads you will get ~600KBps.

For the migration if it's sequential (depending on filesystem layout), the performance can be different, up to maximum streaming performance of like 100MBs for large sequential reads.

Then 2x for your RAID config.

[–] bonaventura84@alien.top 1 points 1 year ago

That is the thing, my total IOPS are less than 150, with 4 disks in RAID 10 I believe I should get 300IOPS due to mirroring. If you look at the graph, red line is transfer in kbps and blue latency, why is it dropping when disk is highly utilised? I will post htop when I’m back from work.

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