The setup is two ESXi 5.5 hosts, one is the main host with three live servers and the second is the backup host with three server replicas, Acronic Applicance and vCenter Server. There is a separate physical machine used as the backup target for the scheduled backup tasks. In addition to backing up to the physical target the three virtual servers are replicated to the secondary host each night.
Nightly backups of the three virtual machines using the Acronis appliance were failing and the Acronis appliance was powering off. According to the Acronis log it was running out of space while running the backups. Normally it is just a matter of deleting all the snapshots using vSphere Client but this time one of them just would not delete.
After reloading the vSphere client one of the replica VMs had a warning saying that it’s disks needed to be consolidated. Several attempts resulted in a error saying the disk images were locked. The Acronis appliance was turned off but it turns out that it was locking files relating to the replica VM. I had to boot and then shutdown the Acronis appliance three times before it would release the lock on the files and the consolidation worked perfectly followed by the removal of the snapshot.