Some links and graphs on ESXi capping/throtteling disk speeds
Posted by jpluimers on 2022/01/06
As promised in “Solution” on ESXi 6.7 smartinfo throwing error Cannot open device, here are a few links in capping throttling disk speeds by ESXi followed by a few graphs of my own:
- GUI operations might be capped, try
dd: [Wayback] datastore – How can I speed up file tranfers on local storage in vSphere 5? – Server Fault
I never got any official confirmation for this, but I believe the I/O is capped (or at least de-prioritized) for datastore copy/move operations from the GUI as I have seen rather similar behaviour in different ESXi environments on from version 3.5.
- [Wayback] Solved: ESXi disk performance, possibly capped? – VMware Technology Network VMTN
Question:
When I copy a 3GB ISO file from the raid set to the sata disk, the average disk transfer is 50MB/sec. This puzzles me, because the SATA disk can do 100MB/sec easy. When I start a second copy, the average disk transfer doubles to 100MB/sec.
…
Answer:
File transfer speeds are capped in the console so you will not be able to get maximum speeds
My own observations on ESXi 6.7 update 3:
- One rsync operation:
1 rsync from 860 EVO SSD to 960 PRO NVMe
- Two rsync operations:
2 rsync from 860 EVO SSD to 960 PRO NVM
- Resume actions were about 10 times faster than the single rsync read speeds:
Resume action
- Suspend actions were between 4 and 6 times faster than rsync write speeds:
Start of suspend action
Finish of suspend action
For each rsync operation, I had a separate SSH session going, and the speed doubled.
The resume action of all Virtual Machines was almost a flat speed curve.
The suspend action of all Virtual Machines started fast (when all machines were suspending) and finished slower (when only the largest virtual machines were still suspending)
–jeroen
The Wiert Corner - irregular stream of stuff 
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