What the IO? Optimal Azure Virtual Machine IO ♥ Calculator

Azure Virtual Machine Disk & VM Throughput Calculator

Jump to the calculator: Calculator


What is this calculator?

This calculator takes the Azure Disk and Virtual Machine IO throttle limits and puts them into a handy calculator so you can see what sort of performance you could *theoretically* get by changing the disks, the type of caching or the type of machine.

What IO limits are there?

Each type of disk has a throughpout limit and each type of virtual machine has a limit for the amount of IO that it serves from its cached pool and from its uncached pool of storage. You can mostly choose whether to use cached or uncached and can mix the two types to increase your total IO throughput. We have seen up to 3,600 MBps on a GS 5 by using the correct disk striping and cache configuration. In fact you can get even higher throughput if you use the cache because IO throttle limits aren't applied to anything served from the cache so the only real limit is the CPUs and how much data they can process.

What happens if I reach a throughput limit

Basically the disk requests get slower as anything over and above the throttle limits are held up until there is some availability to provide them. If you are using notepad then, meh, if you are using a mission critical sql server then, not meh

What vm's / disks does this work with?

I have only included the data for machines which can support premium disks and have only included premium disks. If you are not thinking about premium disks then there is probably no need to do any IO calculations as your performance will be poor for any decent workload. Including standard disks is more complicated as Microsoft don't provide figures on throughput, just how many IOPS each virtual machine can handle and the performance is not guaranteed, unless you use premium disks.

Who wrote this?

me :)

I don't understand and I need to see how fast the disks will be on an XX Azure Virtual Machine, will you help me?

yes, find my details here

Why doesn't this look anything like the rest of the blog site?

Well I was going to shove it somewhere on a cool url like https://whattheio.azure.io but then I thought it would cost me like £0.00 to host it on the site I already had :)

How do I use the calculator?

See the instructions