An example warning message is: WARNING - Unplug of OpaqueRef:62293bfe-c76e-71d4-533d-090699d39fcf failed
PHD VBAs configured with multiple vCPUs on Citrix XenServer v6.0 may encounter intermittent warnings when attempting to automatically remove snapshots. An example warning message is:
WARNING - Unplug of OpaqueRef:62293bfe-c76e-71d4-533d-090699d39fcf failed: INTERNAL_ERROR
This issue appears to be related to a failure in Citrix API call (hot unplug process). PHD has been in contact with the Citrix development team to attempt to discover the root cause of this issue. A timetable for a fix is not currently available.
A workaround for this issue is to first reconfigure the PHD VBA to use a single vCPU. Depending on your specific hardware and environment, 1 vCPU will provide full throughput of up to 8 streams.
To find the optimal number of streams, run your backup job multiple times, incrementing the number of streams by 1 each run. Once the vCPU has saturated, you will see an increase in job elapsed time and a degradation of I/O throughput as reported in the Job Details.
In addition to snapshots being automatically removed, the leaf coalesce procedure for XenServer will help with any cleanup process by regaining free space.
Note that prior to XenServer 6.0, multiple vCPUs were not supported for Debian-based VM guests.