3ware 9xxx cards have a finite number of ports, typically, 8, 12, or 16.  Each port may have:

• One drive attached
• No drive attached

If a drive is attached, it may be:

• Part of a raid unit (u0, u1, u2, etc.)
• A hotspare spare to a raid unit
• Exposed through the 3ware card (JBOD)
• Unused

When drives are assigned to a unit, that unit will have a total of X GB of storage where N is the number of drives and S is the size of the smallest drive:

• RAID 0: X = S * N
• RAID 1: X = S
• RAID 5: X = S * ( N - 1 )
• RAID 6: X = S * ( N - 2 )

The space of one RAID unit may be used for:

• One storage volume
• One boot volume and one storage volume

The single storage volume is most common.  Having a seperate boot volume is only necessary if:

• You are booting off of that Unit (u0, u1, u2, etc.)
• The total storage provided by that unit (X above) is greater than 2TB.

Volumes in excess of 2TB must have a  GPT disk label, and GPT labeled disks aren't bootable.  If you have a RAID array that exceeds 2TB we will create a smaller boot volume to overcome this limitation.

Each volume will appear to the OS as another "hard disk" in that it will have its own device name under /dev (/dev/sda, /dev/sdb,/dev/sdc).  Do not confuse volumes in the 3ware configuration with partitions or LVM in the OS.  The OS can not tell a boot volume and storage volume are part of the same unit.  3ware volumes have nothing to do with the Logical Volume Manager.