Macbook pro, disk utility and external hard drive I have a Macbook Pro running on Lion.  My external hard drive is a Buffalo and used as data backup only, and is formatted to Macs.

I have used the ext. hard drive for two years with no issues. I am considering running "disk utility" (specifically "verify disk") to check its health.  Is there a minimum or maximum amount of times you can run it on an external hard drive?  I am aware of the different types of software you can buy, but running "disk utility" on an external hard drive is my only option right now.
Internal or external makes no difference. it wont damage the disk in any way, it does not use up "write-cycles".
the only useless option would be running verify permissions if you dont have an OSX installation on it.