Running Mac OS X Tiger

RAID

Another feature that Disk Utility and its related command-line tools enable is the use of Redundant Array of Independent Disks (RAID), where multiple physical disks are combined into one virtual disk. In general, RAID solutions are designed for increased data availability and integrity. They trade the overhead of maintaining data across a set of disks for the fault tolerance that using multiple drives can provide.

There are several types of RAID in use today. These are:

RAID 0

Data is striped across two or more disks giving increased I/O performance; if each disk is on a separate disk controller, this allows for large virtual disks. This type of RAID provides no protection against disk failure. If a disk fails, all the data on the disk set is lost.

RAID 1

Data is mirrored across two drives, giving complete data redundancy. If one disk fails, the other still has all the data needed to keep going.

RAID 3, RAID 4, RAID 5

Multiple disks (three or more) are used to both stripe data for performance and to keep parity information to provide for redundancy in case a disk fails. Because data is split and duplicated among many disks, this type of RAID requires significant computation power.

Mac OS X provides support for RAID 0 (striping) and RAID 1 (mirroring). Both types of RAID can be performed with acceptable performance in software. The other forms of RAID are not supported in software, as the increased overhead would create too large a performance hit to be worthwhile. If you require ...