Red Hat Knowledgebase

A RAID array is an array of multiple hard drives which provide data security through redundancy and can also provide increased I/O performance in certain usage scenarios.

When one disk in a mirrored RAID array fails it is necessary to replace that disk with another one. The machine generally must be powered down in order to perform hardware maintenance, although some machines support hot swapping of SCSI drives.

Once the new drive has been added to the system physically, you should issue the command:

# raidhotadd /dev/mdX /dev/[s|h]dX

Where X is the letter of your SCSI (s) or IDE (h) drive. For exmaple, /dev/sdb or /dev/hdc. This will begin the rebuilding process. The current status and estimated time remaining in the rebuild can be found by issuing the command:

# cat /proc/mdstat

For more information on RAID arrays and their administration, consult the Linux Documentation Project's Software-RAID-HOW-TO at http://www.tldp.org/HOWTO/Software-RAID-HOWTO.html