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About Windows NTBased Disk Mirroring and Duplexing

SQL Server 2000

About Windows NT- and Windows 2000-Based Disk Mirroring and Duplexing

Microsoft® Windows NT® and Windows® 2000-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 and Windows 2000 mirrored volume implement 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. Mirrored volume is a feature of Windows 2000. On a dual-boot computer, they are not accessible when running the Microsoft MS-DOS® operating system.

Windows NT–based disk mirroring, or duplexing, and Windows 2000 mirrored volumes offer better write performance than Windows NT–based disk striping with parity and Windows 2000 RAID-5 volumes. They also require less system memory and do not show performance degradation during a failure.

The entry cost of Windows NT and Windows 2000-based disk mirroring or duplexing is lower because they require only two or more disks (compared to disk striping with parity and RAID-5 volume, which require three or more disks). However, mirroring provides less usable disk space (compared to disk striping with parity or RAID-5 volume), 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. Mirrored volumes are set up and managed using the Windows 2000 Disk Management application, which can be started from the Computer Management program.

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

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

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