HyperV types of Virtual Hard disk

There are three known types of virtual hard disk in HyperV: Fixed, Dynamic and Differencing.

Fixed Disk are used in production setups. As the name suggest, the amount of disk space you set is the amount of disk space that hyperv will allocate right away.

Dynamic disks starts off small but will expand to the maximum size specified in the setup. If you run out of space as the dynamic disk is expanding, the Virtual machine will pause. Useful for test bed scenarios and not in production environmnents as this will slow the I/O of the server.

Differencing Disks is a disk that stores the changes to a parent disk. If you want to setup multiple versions from a single parent, the use of differencing disk provides the smallest disk footprint. Ideal only for testbed scenarios.