Using RAID-5 volumes

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Using RAID-5 volumes

A RAID-5 volume is a fault-tolerant volume with data and parity striped intermittently across three or more physical disks. If a portion of a physical disk fails, you can recreate the data that was on the failed portion from the remaining data and parity. RAID-5 volumes are a good solution for data redundancy in a computer environment where most activity consists of reading data.

You can create a RAID-5 volume using hardware- or software-based solutions. With hardware-based RAID, an intelligent disk controller handles the creation and regeneration of redundant information on the disks that make up the RAID-5 volume. Windows Server 2003 operating systems provide software-based RAID, where the creation and regeneration of redundant information on the disks in the RAID-5 volume is handled by Disk Management. In either case, data is stored across all members in the disk array.

In general, hardware-based RAID offers performance advantages over software-based RAID because hardware-based RAID incurs no overhead on the system processor. For example, you can improve data throughput significantly by implementing RAID-5 through hardware that does not use system software resources. This is accomplished by using more disks at a given capacity than would typically be available in a conventional storage solution. Read and write performance and total storage size can be further improved by using multiple disk controllers.

RAID-5 volumes have better read performance than mirrored volumes. When a member is missing, however, such as when a disk has failed, the read performance is degraded by the need to recover the data with the parity information. Nevertheless, this strategy is recommended over mirrored volumes for programs that require redundancy and are primarily read-oriented. Write performance is reduced by the parity calculation. A write operation also requires three times more memory than a read operation during normal operation. Moreover, when a volume fails, reading requires at least three times more memory than before the failure. Both conditions are caused by the parity calculation.

RAID-5 volumes include one parity block per stripe. Therefore, you must use at least three disks, rather than two, to allow for the parity information. Parity stripes are distributed across all the volumes to balance the input/output (I/O) load. When regenerating a RAID-5 volume, the parity information with the data on the healthy disks is used to recreate the data on the failed disk.

For step-by-step information about how to create and repair RAID-5 volumes, see Manage RAID-5 Volumes.

For information about which operating systems support RAID-5 volumes, see Partition styles.

For more information about mirrored volumes, see "Disk Management" at the Microsoft Windows Resource Kits Web site.