[CentOS] software raid1 syncing

Fri Jul 3 20:41:45 UTC 2009
Les Mikesell <lesmikesell at gmail.com>

Steven Vishoot wrote:
> hello all,
> I have a setup that is raid 1 and put the mirrored drive back in and now it is still showing as degraded saying: raid1: raid set md6 active with 1 out of 2 mirrors with this message on all the raids.i know i am wrong by saying this but i thought putting in the driving and rebooting would start the re syncing itself. what do i have to do to add this back in, i am so confused with this process.

A 'cat /proc/mdstat' will show which partitions are active in each md set.  Use 
'mdadm --add /dev/md_device /dev/partition_device'
to add back the missing partitions, being careful to match up the right device 
names for the raid sets and partitions.  This will start a sync with the newly 
added and you can watch the progress with 'cat /proc/mdstat'.  I'm not sure 
exactly what conditions trigger an automatic sync and what requires the manual 
one but if the system goes down cleanly they will pair up at reboot as long as 
the partition type is FD.

   Les Mikesell
    lesmikesell at gmail.com