Backup Versus Server Performance On Windows Server 2008
Slow performance on a Server 2008 Hyper-V server during the day? Is it configured to use the built in Windows Backup and have you recently updated to Server 2008 SP1? If so, there may be an easy solution, but it will increase the backup time. we've had similar issues of late with some of our customers, it's to do with the way the backup now works in Server 2008 R2 SP1, it seems to use more resource than before the service pack.
In a Hyper-V environment, Windows Server backup typically runs on the Hyper-V host machine so that it can conveniently back up all virtual machines at the same time while also having access to the external USB drives used as the backup target. It can be configured 2 ways – increased backup performance or increased server performance. If you go for increased backup performance, it basically has to keep track of every change made throughout the day on each VM. This seems to slow all the VM's down – we've noticed it especially on machines running SQL Server
So, the recommendation is to go for increased server performance instead – this means the backup has to run a full backup every night from then on and this may not be appropriate for your environment, but it does maximise server speed during normal operation.