When you connect several hard disks together and configure the hard disk controller to access them in a predetermined pattern, you create what is known as a disk array.  Disk arrays are used to increase security, performance, or reliability.  They provide faster input and output rates than single large-capacity drives, because the files are stored on individually addressable disks and can be found more quickly during I/O requests.

The amount of security, performance, and improved reliability depends on the application programs that are running and the type of disk array being used.  The type of disk array depends on the data-storage patterns supported by your hard disk controller, operating system, and application programs.  (Your PC Server 500 supports RAID levels 0, 1, and 5.)

Subtopics:
Internal Disk-Array Subsystems
RAID Technology
        Hard Disk Drive Capacities
           Hard Disk Drive Mapping
        Additional Storage Capacity
        Logical Drives
        Improved System Performance
Disk Array Adapter Features
        Overlapped Input/Output Operation
        Interleave Depth/Stripe Unit
        Queue Depth
        Cache
        Hot-Spare Drive Replacement
        Data Protection
Disk-Array Classifications
        RAID Level 0
        RAID Level 1
        RAID Levels 2, 3, and 4
        RAID Level 5

Internal Disk-Array Subsystems
IBM provides an integrated disk-array subsystem as a standard feature on some models of PC Server 500.  Each disk-array model of PC Server 500 contains an IBM SCSI-2 Fast/Wide Streaming-RAID Adapter/A and two or more 1GB or 2GB hard disk drives.  Your server has space for up to 18 hot swappable hard disk drives.  (You can install one additional SCSI device in bay B, but this bay does not support hot swapping.  The drive in bay B cannot be included in the array, unless no more than 5 drives are installed in bank C.  See the User's Handbook for information about SCSI IDs.)