To expand on the above statement which is somewhat wrong regarding agents, agents are generally used to add functionality that the default product does not have. Most backup products support only one thing by default - backing up another computer's file system. This doesn't add any specific application support. For example say you're running MSSQL, Exchange, or Oracle DB.. You can't backup either of these applications while they are up and running, because the files that comprise of the database are constantly open and changing. Backing up those files would actually be worthless if the application is up. Some people will shut the application down, back up the files, then start the application again. That works great if you can afford that window of downtime. Otherwise you need some technic to back up the application while it's running. Some applications by default do support limited backup functionality. For example you can do a backup to a locally attached tape drive or even to disk - but does not have hooks for the actual backup software you're using.
So often given most applications you have a few options..
1-shut down the app, back up the appropriate files, start the app
2-use functionality built into the app to backup the app to some disk space some where, then the real backup app (arcserver, backup exec, whatever) comes along and backs up those files from the disk. After you can erase them.
3-purchase an agent which is typically software provided that interfaces between the given applications API and the backup product to allow you to backup the product while it's up and running.
Some agents even let you do things you can't normally do. An example is Exchange normally via the MS API's only lets you do a full, incremental, or differential backup. But arcserver and veritas agent's will also let you do mailbox backups which can be useful if you find yourself periodically restoring mailboxes for people. Otherwise you'd have to restore the entire server to a seperate box, export the mailbox, and import it on the real production server. Unfortunetly mailbox backups serve as very poor full exchange backups so most organizations using those products actually back up their exchange server twice. Once with a mailbox backup, and once as a more traditional backup.
Bottom line is an agent almost always adds some type of functionality that the product itself doesnt have.
Otherwise i agree with Rols and he's doing a good job replying to you =). I've used all the various backup products except maybe Legato (used it a little but not much). Arcserv and Backup Exec are comparible if you ask me. Stick with what you know.
If you only have 5 + 2 servers then it's probably not time to make the plunge yet for a dedicated backup server and tape library or auto changer. Depends on your budget.. Would it be easier to manage your backups? Sure but i wouldnt spend that money until i found myself anticipating some significant increase in the number of servers you have or found that swapping tapes daily to be unwieldy.
