Duplicate VSS Snapshot

Q: What happens if you have two different services trying to take a Volume Shadow Copy Service snapshot at the same time?

A: If you have two different services trying to take a Volume Shadow Copy Service (VSS) snapshot of the same resource at the same time, whichever VSS request occurs second will fail and then retry based on whatever retry logic is built in. For example, if I was using Hyper-V Replica to replicate a virtual machine that was configured to take application-consistent snapshots, and Data Protection Manager (DPM) also happened to be backing up the virtual machine at the same time, if the DPM backup occurred first, the Hyper-V Replica application-consistent snapshot would fail and Hyper-V Replica would try again at the next application-consistent interval.