Looks like I have found the answer myself, needed to create an advanced disk storage disk pool that uses an advanced disk storage unit. I was only able to create an advanced disk storage unit and storage pool by using the wizard "Configure Disk Storage Servers", not by selecting "New", Storage Unit at the storage unit console tree.

Can someone though explain why this needed a "disk storage server" for the advanced disk pool?

Also, need to know how I can add another drive to an exisiting storage unit on the same media server.

You can add another disk to ADVANCE DISK UNIT only. For Basic i believe it has to be done at Storage level only within NBU there is no way to do unless to create new one. It is better to keep 1 STU per PHYSICAL HARD DISK (to get maximum read/write operations) Having multiple STU in different logical part would not be efficient to achieve performance

Please refer to these documents:

Best practice for configuring AdvancedDisk:
  http://www.symantec.com/business/support/index?pag...

NetBackup 7.5 AdvancedDisk Storage Solutions Guide:
  http://www.symantec.com/business/support/index?pag...

About SLP and Disks:
SLP does not work with BasicDisks. It has always been this way.
Some choose to use AdvancedDisk and MSDP (deduplication) disks so that SLP can be used.
I could only guess that one of the reason is that these non-BasicDisk disk tapes require the purchasing of Enterprise Disk/Dedup licenses.

need to know how I can add another drive to an exisiting storage unit on the same media server.

With AdvancedDisk, you can add additoinal volumes to an existing AdvancedDisk pool (Merging disk pools). Please refer to the above documents for details.

Can someone though explain why this needed a "disk storage server" for the advanced disk pool?

About the storage server paradigm, if you run the following command in admincmd:
  bpstsinfo -serverinfo

Surprise! A BasicDisk is actually also managed by a BasicDisk Storage Server, just like other disk types. It is just that this secret storage server entity is hidden from view unless you type this command.
So a BasicDisk still needs a storage server. In this sense, a BasicDisk is no different than other disk types.
With BasicDisks, the storage server is automatically configured for you when you create a BasicDisk Storage Unit.

Hi,

Thanks, I'm using advanced disks now, what I need to do is add another hard disk to an exisiting "Storage Unit".. I'm not looking at creating multiple storage units within one physical disks, that is for sure an I/O concern,, but multiple physical disks within a storage unit should not be an I/O concern, right?