Disk units are assigned to a disk pool on a storage unit basis. The system treats each storage unit within a disk unit as a separate unit of auxiliary storage. When a new disk unit is attached to the system, the system initially treats each storage unit within it as nonconfigured. You can add these nonconfigured storage units to either the system disk pool, basic disk pool, or independent disk pool of your choosing. When adding nonconfigured storage units, use the serial number information that is assigned by the manufacturer to ensure that you are selecting the correct physical storage unit. Additionally, the individual storage units within the disk unit can be identified through the address information that can be obtained from the DST Display Disk Configuration display.
When you add a nonconfigured storage unit to a disk pool, the system assigns a unit number to the storage unit. The unit number can be used instead of the serial number and address. The same unit number is used for a specific storage unit even if you connect the disk unit to the system in a different way.
When a unit has mirrored protection, the two storage units of the mirrored pair are assigned the same unit number. The serial number and the address distinguish between the two storage units in a mirrored pair.
To determine which physical disk unit is being identified with each unit number, make note of the unit number assignment to ensure correct identification. If a printer is available, print the display of your disk configuration. If you need to verify the unit number assignment, use iSeries™ Navigator to display disk unit properties and check the serial numbers and addresses of each unit.
The storage unit that is addressed by the system as unit 1 is always used by the system to store licensed internal code and data areas. The amount of storage that is used on unit 1 is quite large and varies depending on the configuration of your system. Unit 1 contains a limited amount of user data. Because unit 1 contains the initial programs and data that are used during an IPL of the system, it is also known as the loadsource unit.
The system reserves a fixed amount of storage on units other than unit 1. The size of this reserved area is 1.08 MB per unit, reducing the space available on each unit by that amount.