VM Insights Logical Disk Performance IOPs with Azure SQL Virtual Machine

Question

How does Logical Disks IOPS work on VM Insights? As you know when using Azure SQL on Virtual Machines, inside the VM (at Windows OS level) it uses Storage Spaces to create a virtual disks with disks attached via azure.

So let's say that disk F: in Windows is made of two azure managed disks.
Disk F: (765 Gib) is made of one 256 GiB Premium Disk with 2300 IOPS and one 512 Premium Disk with 2300 IOPS.

VM insights shows a total of 2660.65 IOPS used (P95). How are IOPS calculated in that case? Does disk F: have a limit of 2300 IOPS or is it 4600 IOPS?

Also Logical Disks graphs on VM insights only show a general line graph, not a per disk line. So how can I interpret the graphs? Is it an average of all disks?

Thanks

Answer 1

Hello Christian Fabián

Welcome to Microsoft Q&A Platform, thanks for posting your query here.

When using VM Insights to view Logical Disk Performance IOPs, the IOPS are calculated based on the total IOPS of all disks attached to the logical disk. In your example, disk F: is made up of one 256 GiB Premium Disk with 2300 IOPS and one 512 Premium Disk with 2300 IOPS, so the total IOPS for disk F: would be 4600 IOPS.

Regarding the graph on VM Insights, the Logical Disks graph shows the total IOPS for all disks attached to the logical disk. It does not show a per-disk line graph. The graph displays the average IOPS over a period of time, so you can see how the IOPS usage changes over time.

If you want to see the IOPS usage for each disk separately, you can use the Performance tab in VM Insights to view the IOPS usage for each disk. To do this, select the virtual machine you want to view, and then select the Performance tab. From there, you can select the Disk IOPS chart, which will show you the IOPS usage for each disk attached to the virtual machine.

I hope this helps!