Could not add digest enabled disks
Hot-adding digest enabled disks is not supported in VMware, therefore attempting to back up these VMs will result in an error (could not attach...).
Sample host log:
2013-08-30T17:44:08.677Z [20E92B90 verbose 'Vmsvc.vm:/vmfs/volumes/512f6dc3-f9df2128-2981-3cd92b02c6ba/PHDVBA6_09/PHDVBA6_09.vmx'] Handling message _vmx45: Hot-add of digest enabled disk not supported scsi0:6.
--> Failed to add disk scsi0:6.
Digest enabled disks are the result of Host Caching being enabled for a resource pool. To back up VMs with digest enabled disks, you must first disable host caching for the pool, then power down the affected VM. Then, you must remove all digest related files from the disk directory (for additional details, refer to VMware's knowledge base).