A mirror set creates an identical twin for the selected partition. Creating a mirror set is similar to making a copy of a document by using a copy machine. The original partition is like the original of the document, and the shadow partition is the copy. Unlike a copy machine, however, Windows NT continually updates the shadow partition when any changes are made to the original.
Note
In this chapter and other chapters in the "Reliability and Recoverability" part of this book, the terms original disk and original partition refers to the original partition, and shadow disk and shadow partition refers to the disk or partition that contains the copy.
A stripe set with parity is composed of strips of equal size on each disk in the volume. One of the strips in each stripe is used for parity information.
For a more complete description of mirror sets and stripe sets with parity, including the parity information, see the section titled "Planning a Fault-Tolerant Disk Configuration," in Chapter 4, "Planning a Reliable Configuration."
Because a mirror set or stripe set with parity requires more than one disk, you might have to buy and install additional disks. To increase the redundancy, you might want to buy more disk controllers. It is a good idea to have a spare disk and controller of the same type available. If you are using RAID hardware, follow the manufacturer's installation instructions. When using software fault tolerance, using SCSI controllers is more efficient and provides an additional recovery mechanism of sector sparing. For more information, see "Processing of Disk Errors" in Chapter 3, "Disk Management Basics."
You use Disk Administrator to create and recover mirror sets and stripe sets with parity. When you select one of the partitions of a mirror set or stripe set with parity, Disk Administrator displays information about the volume in the lower left corner of the window. The information looks like:
where
The following table shows the possible status values.
Table 5.1 Disk Administrator status information for stripe sets, mirror sets, and stripe sets with parity
| Stripe set with parity |
|
|
HEALTHY | HEALTHY | HEALTHY | The volume has been initialized, and there are no errors. |
NEW | NEW | NEW | Appears immediately after the volume has been created, but before shutting down the system to begin generation of the volume. |
REGENERATING | INITIALIZING | INITIALIZING | Generation of the volume has been started, but is not yet completed. |
RECOVERABLE | RECOVERABLE | Not applicable | Appears when one of the partitions in the volume has been lost, but the other partition(s) is (are) undamaged. This message also appears when one partition loses synchronization with the other(s). |