Could anyone tell me if Unity server needs to be defragment for a certain period of time. If yes, How long I need to perform a defragment action and the appropriate steps (for the database and windows system files...etc)?
Defragmentation of the file system and SQL isn't really necessary these days - defragmentation of the Exchange mailstore on the back end (presumably running off box) is a different story, particularly if the HD space becomes limited.
Here's a white paper on maintaining Unity that does cover some tasks you need to worry about which might be helpfull:
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.