Avamar: Troubleshooting VMware image backup fails when user snapshot is deleted during backup

VMware image backup failing with the following:

avvcbimage Info <14665>: 1 snapshots are present on this VM:
  *level=1, children=0, ref='snapshot-7553', 'VEEAM BACKUP TEMPORARY SNAPSHOT':desc='Please do not delete this snapshot.''

While backing up one or more of the data disks for a VM, the backup fails with this message:

avvcbimage Info <16041>: VDDK:<date> error -[7FFA0C431700] [Originator@6
876 sub=transport] Reconfigure attempt failed for VM "vm-21" with Vmomi::MethodFault::Exception ("vim.fault.FileNotFound")

avvcbimage Info <16041>: VDDK:VixDiskLib: Unable to locate appropriate transport mode to open disk. Error 13 (You do not have access rights to this file) at 4559.

avvcbimage Info <16041>: VDDK:VixDiskLib: VixDiskLib_OpenEx: Cannot open disk [datastore] vm/vm.vmdk. Error 13 (You do not have access rights to this file) at 4669.

avvcbimage Info <9772>: Starting graceful (staged) termination, VixDiskLib_Open attempt to connect to virtual disk failed (wrap-up stage)

In the example above, the user is backing up the same VM simultaneously using two different backup products. A process deleted users/non-avamar snapshot while Avamar backup was still running causing the disk specified in the work order to be invalid.

Example disk info from work order:

Prior Disk '2001': file(base):'[datastore] vmname/vmname_1.vmdk', backItUp=1
               snapshot file:'[datastore] vmname/vmname_1-000001.vmdk'
               prior size(KB):52428800, current size(KB):52428800, match=1

After Avamar snapshot:

Current Disk '2001': file(base):'[datastore] vmname/vmname_1.vmdk', backItUp=1
               snapshot(base) file:'[datastore] vmname/vmname_1-000001.vmdk'
               snapshot(curr) file:'[datastore] vmname/vmname_1-000002.vmdk'
               prior size(KB):52428800, current size(KB):52428800, match=1

Then the snapshot was deleted by outside process vmname_1-000001.vmdk file was deleted and thus backup failed with the file not found.

This could also occur if a normal user snapshot was deleted while backups are running.

Do not delete snapshots while Avamar backup is running. To avoid snapshot collision like this case, we recommend to only backup a given VM using a single snapshot based backup product. If two snapshot backup products are used on the same VM, they ensure no schedule overlap.