@Gostev, thank you, I have a support case for this issue, # 5162648.
I'd be very interested to hear of any workarounds that don't require downgrading VMs to VM Hardware version 7
Well... when you say certain VMs.. I see the CBT error happening basically on all VMs. Including new VMs...
If I right click a cluster, create a brand new VM with 2 fresh VMDKs, Version 8 virtual hardware, the CBT failure predictably comes up at the 2nd backup for any new VM I make. When I create a new VM with version 7 hardware and try to back that up, the CBT seems to work correctly on freshly created Virtual Hardware Version 7 VMs.
(you won't see this in your PowerCLI test because your script does not mount disks with VDDK)
Well, that's very interesting... I find that indeed, when I let Veeam create the temporary snapshot,
and wait for Veeam to apply its "reconfigure virtual machine" tasks on the source proxy VM, presumably hot-adding the VMDKs,
_After_ veeam does its hot adds / mounts, I am able to see the same error raised through power shell, to a query that worked moments before.http://pastebin.com/W8fwZsbS
If I create a snapshot of my own, or make queryChangedDiskAreas queries during a backup after Veeam creates its snapshot, but before Veeam does its "reconfigure VMs" on the hot-add backup proxy VM, the query made from powershell gets a Change block response, instead of an error.