Why isn't Windows Server allowing me to create a storage tier?
There are two main circumstances that prevent Windows Server 2012 R2 administrators from being able to create a storage tier. The first reason has to do with having the proper hardware. In Windows Server 2012 R2, the available solid-state drive storage has to match the storage layout that you select.
When you work through the New Virtual Disk Wizard, the wizard has you select a storage pool, name the virtual hard disk you are creating, and then choose whether or not you want to create tiered storage for the virtual disk. It is not until the next screen that you have the option of choosing your storage layout. If you have chosen to use storage tiers, the available choices for the storage layout will be directly impacted by the number of hard disk drives (HDDs) and solid-state drives (SSDs) that are available within the storage pool.
Suppose, for instance, that you want to build a three-way mirror that uses tiered storage. In order to do so, your storage pool will need at least three HDDs and three SSDs. If you have three HDDs, but only one SSD, creating a three-way mirror with tiered storage will not be an option.
The other issue that can stop you from creating a virtual disk that uses tiered storage has to do with incorrectly identified hard disks. Some systems have difficulty differentiating between HDDs and SSDs. When this happens, you will need to use PowerShell to specify the type of disks in your system. You can do so by combining the Get-PhysicalDisk cmdlet with the Set-PhysicalDisk cmdlet. When you specify the Set-PhysicalDisk cmdlet, you can use the MediaType parameter, followed by either SSD or HDD. This will allow you to specify the physical media type of the disk.