There are a lot of situations thinkable in which someone wants to move a running virtual machine on Hyper-V to a different storage location without downtime. For example because the volume is running out of space, or the performance of the diskset is not sufficient, or for moving to another storage array.
VMware vSphere offers storage migration functionality (Storage VMotion)without having any downtime which is a much appreciated feature by system administrators. Selected running virtual machines can be re-located to a different storage location during office hours with no downtime.
Microsoft Hyper-V however does not offer a feature to move running virtual machines to another disk location. When using SCVMM 2008 R2 Quick Storage Migration can be used to move virtual machine hard disk files to another location. See this article titled Using Quick Storage Migration in System Center Virtual Machine Manager 2008 R2 how this can be done. However using Quick Storage Migration will result in some downtime which can be several minutes.
If your organization is using Hyper-V and has a need for live storage migration a company called Melio will soon have a solution. The soon to be released Melio Unified Storage Platform has a RAID1 Mirroring feature which enables a Melio FS formatted volume to be mirrored on the fly. When both source and target volume are in sync, you can decide which volume will be the new active volume. During the sync and switch over to the new volume virtual machines will remain online with no downtime. The volume will need to be a Melio FS formatted volume. The RAID1 mirror is not available on CSV volumes formated with NTFS. Also it is not possible to migrate one or a few individual virtual machines using Melio’s mirroring feature. All virtual machines hard disk files located on the to be discontinued volume will be migrated. After the migration has finished, the new volume can be resized using the Melio LaScala disk manager.
Besides this feature Melio FS offers a lot of other advanced feature not available in Microsoft CSV volumes like Storage Quality of Service.