Drive Mirroring - Compaq N2400 - TaskSmart - 1 GB RAM Administration Manual

Drive Mirroring

The operating system drives are protected by RAID 1, or drive mirroring.
RAID 1 is the highest-performance fault-tolerance method. RAID 1 is the only
method for fault-tolerance protection if only two drives are installed or
selected for an array. Drive mirroring creates fault tolerance because both
drives are exact copies of each other. If one drive fails, the other immediately
takes over. RAID 1 is an expensive fault-tolerance method because 50 percent
of the drive capacity is used to store the backup copy.
IMPORTANT: The configuration that Compaq supports uses RAID 1 on the system drives in
a two-drive RAID set.
RAID 1 requires an even number of drives. To improve performance in
configurations with more than two drives, the data is striped across the drives.
This is referred to as RAID 0+1, or RAID 10.
If a drive fails, the mirror drive provides a backup copy of the files, and
normal system operations are not interrupted. For example, consider the
following scenario:
When eight drives are used in a RAID 0+1 configuration, each RAID 0
subarray consists of four drives. Each of the four drive subarrays is a mirror of
the other four drive subarrays.
If there is a single drive failure, the data remains intact. A single drive failure
causes an individual subarray to stop working. RAID 0 is not fault tolerant.
One drive failure results in the loss of the affected array. The mirrored RAID 0
subarray is an exact copy, allowing the system to continue to work.
However, if both subarrays fail, all data is lost. The dual failure causes the
entire RAID 0 + 1 array and Array Configuration Utility (ACU) to fail. If the
failure is on the operating system drive, the system stops completely.
IMPORTANT: If two drives being mirrored to each other both fail, data loss occurs.
RAID Levels B-3