Shared VHDX was introduced in WS2012 R2 to enable easier and more flexible deployments of guest clusters; that is, a cluster that is made from virtual machines. The guest cluster allows you to make services highly available, because sometimes a HA infrastructure is just not enough (we are supposed to be all about the service, after all).
We’ve been able to do guest clusters with iSCSI, SMB 3.0, or Fiber Channel/FCoE LUNs/shares but this crosses the line between guest/tenant and infrastructure/fabric. That causes a few issues:
- It reduces flexibility (Live Migration of storage, backup, replication, etc)
- There’s a security/visibility issue for service providers
- Self-service becomes a near impossibility for public/private clouds
That’s why Microsoft gave us Shared VHDX. Two virtual machines can connect to the same VHDX that contains data. That disk appears in the guest OS of the two VMs as a shared SAS disk, i.e cluster-supported storage. Now we have moved into the realm of software and we enable easy self service, flexibility, and no longer cross the hardware boundary.
Shared VHDX was a version 1.0 feature in Windows Server 2012 R2. It wasn’t a finished product; Microsoft gave us what they had ready at the time. Feedback was unanimous: we need backup and replications support for Shared HDX, and we’d also like Live Migration support.
The Windows Server vNext Technical Preview gives us support to replicate Shared VHDX files using Hyper-V Replica (HVR). This means that you can add these HA guest clusters to your DR replication set(s) and offer a new level of availability to your customers.
I cannot talk about how Microsoft is accomplishing this feature yet … all I can report is what I’ve seen announced.