We are writing to you to let you know of an issue with the recently released NetVault Backup Plug-in for Hyper-V 10.5 and provide temporary solutions while we work to address the issue. In Plug-in for Hyper-V 10.5, whitespace (unallocated blocks of data) in Hyper-V-based dynamically expanding VHD/VHDXs are not ignored during backup. This issue impedes backup performance.
The reading of whitespace and possible backup performance degradation depends on the amount of whitespace in the VHD/VHDXs. The more whitespace present in the VHD/VHDXs, the longer a backup takes in comparison to previous versions of the Plug-in for Hyper-V.
Customers who back up to tape, VTL, or NetVault SmartDisk see the most performance impact, while customers who back up to a Dell DR Series appliance, or DD Boost see the least amount of impact. This is due to source side deduplication technology, which handles whitespace more efficiently.
Fixed VHD/VHDXs are not affected by this issue because the Plug-in for Hyper-V has always backed up the whitespace of fixed disks.
There is no workaround for this issue. If you use dynamically expanding VHD/VHDXs, Dell recommends that you use Plug-in for Hyper-V 10.0.1, unless a specific feature of version 10.5 is required. A list of new features can be found in the release notes.
Dell is working to produce a patch for this issue. The schedule for this patch has not been identified, but resolution is a high priority. For additional status information, see Knowledgebase Solution.