mounting RAID devices on boot

if you already have a software RAID configured with mdadm it won't reassemble automatically on each boot. in order to have it reassembling do the following:

mdadm --detail --scan > /etc/mdadm.conf 

That's pretty much it!

Other useful commands:


Creating a RAID:

mdadm -Cv /dev/md1 -level=1 -n2 /dev/sdb1 /dev/sdc1

watching the building/rebuild status

cat /proc/mdstat

Check the RAID state:

mdadm -D /dev/md1

Simulates a failed drive:

mdadm /dev/md1 -f /dev/sdc1

Add a new drive (partition) to replaced the failed one:

mdadm --manage /dev/md1 -a /dev/sdb2

To reuse the failed drive one have to remove it and add it again to the array:

mdadm --manage /dev/md1 -r /dev/sdc1
mdadm --manage /dev/dm1 -a /dev/sdc1

Stopping a RAID:

mdadm -S /dev/md1

To "remount" a stopped or un-assembled RAID:

mdadm --assemble /dev/md1 /dev/sdb1 /dev/sdc1

OR

mdadm --assemble --scan

one more time the gentoo wiki has thousands of good info regarding software-based RAID:
http://en.gentoo-wiki.com/wiki/RAID/Software