Red Hat Knowledgebase

The raidhotadd command will rebuild your RAID array once the drive has been replaced.

Before running raidhotadd, you need to determine the layout of your RAID array. You can view this by looking at the /etc/raidtab file, for example:

# cat /etc/raidtab raiddev /dev/md0 raid-level 1 nr-raid-disks 2 persistent-superblock 0 chunk-size 8 device /dev/hda1 raid-disk 0 device /dev/hdb1 raid-disk 1

The above example shows that your RAID device is /dev/md0 and consists of two partitons: /dev/hda1 and /dev/hdb1. The RAID level on this device is RAID 1.

Assuming that the second drive in the RAID array (/dev/hdb) failed and was replaced. To rebuild the mirror for the RAID device, you need to issue the following command:

raidhotadd /dev/md0 /dev/hdb1

This will start the rebuild process on that RAID device. If you want to watch the progress of the rebuild, you can issue the command:

watch cat /proc/mdstat

Repeat this process for each RAID device in your system.

NOTE: Before performing these steps please make sure your replacement hard drive is properly partitioned using tools such as fdisk. Also, make sure that the partitions on the disk are of type Linux raid auto (type 0xfd). Otherwise, the rebuild operation will fail!