[CentOS] RAID 1 Post Install

Tue Dec 2 17:29:06 UTC 2008
Tom Brown <tom at ng23.net>

> Is there a GUI like Disk Druid for initializing hard drives in 
> software RAID 1 *after* the system has been installed?

no need -


    5.6 RAID-1

You have two devices of approximately same size, and you want the two to 
be mirrors of each other. Eventually you have more devices, which you 
want to keep as stand-by spare-disks, that will automatically become a 
part of the mirror if one of the active devices break.

Set up the |/etc/raidtab| file like this:

raiddev /dev/md0
        raid-level      1
        nr-raid-disks   2
        nr-spare-disks  0
        persistent-superblock 1
        device          /dev/sdb6
        raid-disk       0
        device          /dev/sdc5
        raid-disk       1

If you have spare disks, you can add them to the end of the device 
specification like

        device          /dev/sdd5
        spare-disk      0

Remember to set the |nr-spare-disks| entry correspondingly.

Ok, now we're all set to start initializing the RAID. The mirror must be 
constructed, eg. the contents (however unimportant now, since the device 
is still not formatted) of the two devices must be synchronized.

Issue the

  mkraid /dev/md0

command to begin the mirror initialization.

Check out the |/proc/mdstat| file. It should tell you that the /dev/md0 
device has been started, that the mirror is being reconstructed, and an 
ETA of the completion of the reconstruction.

Reconstruction is done using idle I/O bandwidth. So, your system should 
still be fairly responsive, although your disk LEDs should be glowing 

The reconstruction process is transparent, so you can actually use the 
device even though the mirror is currently under reconstruction.

Try formatting the device, while the reconstruction is running. It will 
work. Also you can mount it and use it while reconstruction is running. 
Of Course, if the wrong disk breaks while the reconstruction is running, 
you're out of luck."

Taken from