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. provides 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.

The data redundancy method used by RAID-5 volumes is a function of the Boolean operation called XOR (exclusive OR) 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. RAID-5 volumes maintain an XOR value of the total data, which enables the reconstruction of missing data (on a failed disk or sector) from the remaining disks in the RAID-5 volume.

RAID-5 provides data redundancy at a cost of only one additional disk for the volume. Recovery from the failure of a disk in a RAID-5 volume is more time-consuming than for a mirrored volume, however. When you want to recover the space in a RAID-5 volume for other purposes, be sure to back up the information in it first if you want to reuse that information. After you have performed the back up, you can safely delete the volume.

RAID-5 volumes are not available on Windows XP Home Edition or Windows XP Professional and cannot be mirrored or extended. You can, however, use a computer running Windows XP Professional to create RAID-5 volumes on remote computers running Windows 2000 Server, Windows 2000 Advanced Server, Windows 2000 Datacenter Server, or .

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

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