Why does Quest Software recommend against having antivirus software installed on migration workstations?
Antivirus software in general is very invasive, it takes over the operation of the system to such an extent that it has the potential to interfere with pretty much anything. Because migrations are done by moving data through the migration workstation, all of that data is also passing through the antivirus engine, which will have a measurable effect on migration performance. This is even more pronounced if the mailbox being migrated contains a lot of attachments.
There's also the possibility that it could interfere with a migration, and affect migration throughput speeds. This usually doesn't happen, but there are some antivirus configurations that are considerably more pervasive than simply scanning files. Some will prevent access to ports (firewall), lock system files, run anti-spyware utilities that hog memory, etc.
Basically, the decision to use antivirus is up to the customer. We recommend against it so that the workstation can be simplified as much as possible and the possibility of problems is reduced by removing every possible variable that could affect the migration itself.
If Antivirus cannot be disabled, then you must exclude the following folders from scan:
C:\windows\temp and (%TEMP% if different)
C:\Program Files (x86)\Binary Tree\CMT for Exchange