Diskeeper just announced that its deframenter is now certified for Microsoft Hyper-V.
Defragmentation is one of the first and most basic tasks in the computer maintenance routine, but when applied to virtual infrastructures it requires some extra effort.
Any virtual machine can be defragmented at the guest OS level, as any other physical operating system, but its container, the virtual hard disk, is just another monolithic file sitting at the hypervisor / host OS level, and it may be not defragmented as well.
So while the guest OS may be fully optimized, the underlying virtual HD could be not and the resulting disk I/O performance can be poor.
It seems that Diskeeper is the first company to support defragmentation at the host and guest level for Hyper-V, addressing the challenge.