With Symantec Endpoint Protection 11.0 installed, system backups run slower than usual.
Cause:
In Symantec AntiVirus, scanning files that are being backed up is disabled by default. In Symantec Endpoint Protection, it is enabled by default.
Solution:
To disable the scanning of files that are being backed up, follow the below steps:
In the Symantec Endpoint Protection Manager, go to Policies
Open the Antivirus and AntiSpyware policy.
Select File System Auto-Protect.
Click on the Advanced Scanning and Monitoring button.
Uncheck Scan when a file is backed up. Additionally, further performance improvements may be gained by choosing "Scan when a file is modified" instead of "Scan when file is accessed or modified."
Click on OK to save the change.
From KB -
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2007103008334648