VHDs work on Windows Server 2008, 2008 R2, 2012 and 2012 R2. Hyper-V on Windows 8 also supports it as well as Virtual PC and Virtual Server, remember those? Hence if you want to move your disks around different Windows host versions, VHD is the way to go.
VHDs use a 512 byte block size internally
VHDs are limited to a 2TB
VHDs can’t be resized live.
Microsoft is quite an anxious animal. They put a lot of work into the VHD format, now VHDX, to better compete with VMware. Hence, a lot of improvements were added:
Live resize of virtual disks.
4KB block size, aligns well with modern hard drives (3TB+) which also use 4KB internally. Hence, it’s best to format NTFS partitions using the default cluster size of 4KB.
Improved handling of power failure conditions
Better handling of snapshots
Up to 64TB disk sizes supported
Only supported on Windows 8, Windows Server 2012 and later.
For best backup performance, use BackupChain to back up your VHD and VHDX Hyper-V virtual machines.