When it comes to disks, things may seem straightforward, but there are a few things that can trip you up. First, we need to understand how Azure Virtual Desktop works. The last part of the AVD sign-in process is a Windows login. This is the same function that happens when you log onto your desktop or laptop. Your user is authenticated, and your Windows profile is loaded, and you're dropped onto your desktop. You also need to understand that we have two different kinds of host pools in AVD, Personal and Pooled.

In a Personal Host Pool, you will have a mapping of one user to one Session Host VM. In a Pooled Host Pool, you will have many users logging onto each Session Host VM. In Personal Host Pools, it's generally not recommended to use FSLogix. However, FSLogix is almost always needed in a Pooled Host Pool. We'll cover more about this in a minute. Let's think about these two host pool scenarios with Virtual Machine Disks.

In both cases, the systems performance will be limited by the characteristics of your disks. The main disk characteristics are: capacity, throughput, and input/output operations per second, or IOPS, for short. There are several disk types in Azure to choose from, ranging from Hard Disk Drives to Standard SSDs, Premium SSDs, and Ultra SSDs, with Hard Disk Drives being the lowest cost per gigabyte storage, but also having the lowest performance. In a Personal Host Pool, you have one user logging onto one VM Session Host. That doesn't automatically mean that you should give them a Hard Drive.

All performance in AVD comes down to what the users are doing and the requirements for them to do it. If you don't know the storage throughput and IOPS requirements for your users to run their applications, I generally start with a Standard SSD for Personal Host Pools and a Premium SSD for Pooled Host Pools. Do some real world testing with different users running their applications and see how they feel about it. If everything looks good, you've hit the sweet spot. If it isn't just right, we have some options.

In Azure, the SSD IOPS are based on the size of the disk. The larger the disk, the more IOPS. If your disk performance is slow, the first thing you should think to try is to make your disk larger. This is generally preferred instead of adding more disks to the system because multiple disks will generally have higher cost than a single larger disk. This would also mean that you have more things to manage and protect.

As for Pooled Host Pools, your User Profiles will be using FSLogix, but Disks are important to think through. FSLogix user and office profiles can be configured in one or two ways, and that is to use VHD Locations, which write data directly to your File Share or Cloud Cache. This is where data writes will take place locally on the C:\ drive.

We will go into depth more in a follow-up course so we won't deal with it further here. But since pooled host pools have multiple users logging onto them at the same time, we must have enough disk performance and capacity for all of them simultaneously, as well as in that Cloud Cache configuration, there will be more intense writes happening on the C:\ drive so you may need a larger disk. This is why I also always recommend starting with a Premium SSD for your Pooled OS Disks.