- Random-access storage pool volumes
Random-access storage pools consist of volumes on disk. Random-access storage pools are always associated with the DISK device class. All volumes in this type of storage pool have the same form. - Sequential-access storage pool volumes
Sequential-access volumes are volumes in data is accessed sequentially, one block at a time, one after the other. Each volume that is defined in a sequential-access storage pool must be the same type as the device class associated with the storage pool. 
Preparing volumes for random-access storage pools (AIX, Linux, and UNIX)
Volumes in random-access storage pools must be defined before the server can access them.
Preparing volumes for random-access storage pools (Windows)
Volumes in random-access storage pools must be defined before the server can access them.- Preparing volumes for sequential-access storage pools
For most purposes, in a sequential-access storage pool, the server can use dynamically acquired scratch volumes, volumes that you define, or a combination of both. - Updating storage pool volumes
You can update a volume to reset an error state to an access mode of read/write. You can also update a volume to change the its location in a sequential-access storage pool. or to change the access mode of the volume, for example, if a tape cartridge is moved off-site or is damaged. - Access modes for storage pool volumes
Access to a volume in a storage pool is determined by the access mode assigned to that volume. You can manually change the access mode of a volume, or the server can change the access mode based on what happens when it tries to access a volume.