About Windows NT-based Disk Mirroring and Duplexing

Microsoft® Windows NT®-based disk mirroring and duplexing implement RAID (redundant array of independent disks) features in software, using any hardware compatible with the operating system. Because these are software-based solutions provided with the operating system, they offer a cost advantage.

• Disk mirroring protects against media failure by maintaining a fully redundant copy of a partition on another disk. This provides protection from the downtime and expense involved in recovering lost data and restoring data from a backup storage facility. In a sense, mirroring is continual backup. Mirroring also provides some performance benefits when reading data from disks under heavy I/O loads. Windows NT-based disk mirroring implements RAID 1.
• Disk duplexing is a form of mirroring that provides protection against controller failures (in addition to protecting against media failures) by using a different disk controller on the mirror disk.

Disk mirroring and duplexing are features of Windows NT Server. They are not supported for Windows NT Workstation. On a dual-boot computer, they are not accessible when running the Microsoft MS-DOS® operating system.

Windows NT-based disk mirroring, or duplexing, offers better write performance than Windows NT-based disk striping with parity. It also requires less system memory and does not show performance degradation during a failure.

The entry cost of Windows NT-based disk mirroring or duplexing is lower because it requires only two or more disks (compared to disk striping with parity, which requires three or more disks). However, mirroring provides less usable disk space (compared to disk striping with parity), so the cost per megabyte is higher.

Disk mirroring and duplexing are implemented by using the Windows NT Disk Administrator application, which can be started from the Administrative Tools program group.

For more information about setting up disk mirroring or duplexing, see your Windows NT Server documentation.

Note The term mirroring is frequently used in Windows NT Server documentation to describe both disk mirroring and duplexing.