I have a PostgreSQL running on Windows Server 2008 R2 x64 box. And I have scheduled a backup everyday from the RAID 1 DB disk to a dedicated standalone disk. They are SAS 15k on Dell PERC 6i. I am using the built-in Windows Server Backup for purpose.
The problem is, whenever the backup process is kicked in, the database performance is hogged. I would say almost a 10x of performance reduction.
From the resource monitor, the disk queue is in the double digit range when backing up, and less than 1 during the day. The disk activity is like ~30-50MB/s during backup, so I guess the hardware is acting normally, though wbengine.exe takes up most of the portions.
I think reduce the IO priority of the backup process would be an answer, but I couldn't find a way to. Tuning process CPU priority does not seems to help.