Azure Ultra disk - sharing disk increases latency by 48%

Martin Kallukalam 5 Reputation points
2023-05-05T19:11:35.9633333+00:00

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?

Azure Disk Storage
Azure Disk Storage
A high-performance, durable block storage designed to be used with Azure Virtual Machines and Azure VMware Solution.
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  1. Sumarigo-MSFT 43,486 Reputation points Microsoft Employee
    2023-05-08T15:54:26.62+00:00

    @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.

    Please do not forget to "Accept the answer” and “up-vote” wherever the information provided helps you, this can be beneficial to other community members.