Howto rebuilding a RAID array after a disk fails

Q. I have two disk-mirrored array, suppose if one of my disk in mirrored RAID array fails, then I will replace that disk with new one (I have hot swapping SCSI drives). Now question is how I rebuild a RAID array after a disk fails.

A. A redundant array of inexpensive disks, (redundant array of independent disks) is a system, which uses multiple hard drives to share or replicate data among the drives. You can use both IDE and SCSI disk for mirroring.

If you are not using hot swapping drives then you need to shutdown server. Once hard disk has been replaced to system, you need to use used raidhotadd to add disks from RAID-1, -4 and -5 arrays, while they are active.

Assuming that new SCSI disk is /dev/sdb, type the following command:# raidhotadd /dev/mdX /dev/sdbReplace /dev/mdX with actual raid device name (e.g. /dev/md0). While array is under construction, you can see progress and other information by typing following command:# cat /proc/mdstat

See also:

• Surviving a Linux Filesystem Failures
• Above two commands are more than sufficient to solve your problem. However, I recommend reading The Software-RAID HOWTO for more information.

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