Passive Copy Of Database Getting Hammered During VSS Backups

Check out checksum throttling:

The Online Maintenance Checksum task can be enabled via the registry:

Registry Hive: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\ParametersSystem
DWORD Key: Online Maintenance ChecksumDWORD Value: 1 (enabled), 0 (disabled)DWORD Key: Throttle ChecksumDWORD Value:

For more information, please see: http://technet.microsoft.com/en-us/library/bb676537.aspx