Azure Ultra disk - sharing disk increases latency by 48%

Question

I am running a benchmark test with Azure Ultra disk for latency and IOPS.
I find a very odd behavior. very consistent and able to recreate any number of times
Test setup: Linux VM 8.7 D8s v3

500GB Ultra disk. Configured with 5000 IOPS. 200MB/s. Disk access created so that disk is accessed over private endpoint.
fio tool : iodepth=1, bs=8k. --rw=randread --direct=1 --ioengine=libaio

Basically I want to hammer the disk with just enough IO to keep it below its provisioned IOPS which is 5000. Hence QD=1 specified for fio so that I am operating the disk in its nominal operating range.

Test1: Disk sharing: disabled : gives me an iostat read latency of .52ms at 1498 read iops

Test2: Disk sharing: 2 : gives me an iostat read latency of 0.77ms at 1071 read iops

[On test 2. I unassign disk, clicked the sharing radio button , save it and reassign the disk to VM . I dont even have a 2nd VM mapped to this disk]

I repeated the same above two tests, at least 5-7 times with same result which shows that just enabling disk sharing increases latency consistently by 45-50%

Can someone tell me if this is by design or what is going on here?

Answer 1

@Martin Kallukalam Welcome to Microsoft Q&A Forum, Thank you for posting your query here!

We need a deeper investigation on this issue, Need to know exactly is causing problem, it's completely unclear ,There could be several reason for the latency,

I would recommend you to contact support, so If you have a support plan, I request you file a support ticket, else please do let us know, we will try and help you get a one-time free technical support. In this case, could you send an email to AzCommunity[at]Microsoft[dot]com referencing this thread as well as your subscription ID. Please mention "ATTN subm" in the subject field. Thank you for your cooperation on this.

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