Testing a Fault-Tolerant System
If the computer has software fault-tolerant volumes, test your configuration by simulating the failure and replacement of a disk.
Even though fault-tolerant volumes continue to work when one disk has failed, there is no fault tolerance until you install a replacement disk. A second disk failure during this interval will result in loss of data, because data redundancy was lost when the first failure occurred. If a backup disk is not readily available, significant business costs can result from the downtime.
If you have hardware RAID arrays, documentation provided by the vendor needs to describe how to recover from disk or controller failures. Make sure to test that their procedures work for your installation.
Fault tolerance is not an alternative to performing regular backups.