Windows Server Backup Issue

In one client environment we use Windows Server Backup that's built-in to Server 2008 & 2008 R2. It's limited in features however it's highly reliable, fast, and is native to the operating system.

We had one server that continued to fail however. It's running 2008 R2 Enterprise and is a Hyper-V host with about 8 virtual servers. It appeared that it was timing out consistently. We edited the backup job (from the GUI) and could successfully execute the backups without the iSCSI LUN where most of the VMs live and we could do a separate backup with only the iSCSI LUN without error however when we tried to backup the local machine and the iSCSI LUN together it timed out. Inside of the logs (Application) an error in Backup: Event ID 521, The backup operation that started at '‎2010‎-‎06‎-‎27T17:27:23.225000000Z' has failed because the Volume Shadow Copy Service operation to create a shadow copy of the volumes being backed up failed with following error code '2155348001'. Please review the event details for a solution, and then rerun the backup operation once the issue is resolved.

Lots of searching revealed no simple remedies, however I finally found one item near the end of a post here that gave me something else to try.

After creating the registry mod mentioned, HKLM\Software\Microsoft\CurrentVersion\SPP and then create a new REG_DWORD entry with the value data (hex) being b71b00 (which should create a traditional value of 12000000 which equates to 20 minutes instead of the default 10. No service restarts or anything else, just create that entry. We then kicked off another full backup (local and iSCSI LUN and it's running successfully!