Many computer systems require you to take responsibility for how information is stored and retrieved from the disk units, along with providing the management environment to balance disk utilization, enable disk protection, and maintain balanced data spread for optimum performance.
When you create a new file, you must tell the system where to put the file and how big to make it. You must balance files across different disk units to provide good system performance. If you discover later that a file needs to be larger, you need to copy it to a location on disk that has enough space for the new, larger file. You may need to move files between disk units to maintain system performance.
The IBM i storage management takes responsibility for managing the information in auxiliary storage pools (also called disk pools or ASPs).
When you create a file, you estimate how many records it should have. You do not assign it to a storage location; instead, the system places the file in the best location that ensures the best performance. In fact, it may spread the data in the file across multiple disk units. When you add more records to the file, the system automatically assigns additional space on one or more disk units.