Azure – Why is the Azure VM (D3) Disk I/O crazy slow

azuressdvirtual-machineswindows 10

I have setup a D3 VM running Windows 10 on my Azure account. Unfortunately the Disk speed, on both the C (200GB) and D (100GB Temp) are EXTREMELY low. Less than 1MB/s when viewed through Task Manager while copying over a large folder structure containing about 16000 items.

To be honest I'm not even sure what to try…I guess my plan will be to create a new vhd drive, attach it, and see how it performs but I'm not real hopeful.

I read through this post –> Slow disk performance on Azure Virtual Machine

and

this post –> http://azure.microsoft.com/blog/2014/10/06/d-series-performance-expectations/

They both reference "throttling" which I understand but what I am seeing must be something different as I never approach the level it states of 96MB/s write.

Is this just common knowledge or is it possible I have something configured wrong? A Windows 10 VM bug maybe? I have verified that I did, in fact, chose D3 for my VM size which includes a 200GB local SSD.

Any suggestions on what I can check or try next?

EDIT

Some further info. Here is a screenshot of my Disk Read/Write from the Azure Portal for the last 24 hours.

enter image description here

Best Answer

Some problems here, but besides the possible azure issue you lack a basic understanding of computer storage.

opying over a large folder structure containing about 16000 items.

that is a LOT of files. Likely not a lot of too large files. Lots of folders, lots of metadata.

what I am seeing must be something different as I never approach the level it states of 96MB/s write.

which is totally irrelevant if you waste all your time doing linear IO (which explorer does) with a ton of metadata updates. MB is not IOPS.

Now, I agree you have an issue -because I also see 12k IOPS given - but as administrator you should know that:

  • Copy operations of a lot of files cause a lot of metadata updates which slow things up and

  • Windows Explorer is really slow in that it does things linearly. Split the copy job into multiple smaller jobs that run in parallel and you may see a speed up.

The last one can be significant - Explorer etc. do one file at a time, waiting for certain things to finish. All the while nothing happens. Multiple parallel jobs may simply be - faster.

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