mdadm (multiple devices admin) is an extremely useful tool for running RAID systems. It’s is a tool for creating, managing, and monitoring RAID devices using the md driver. It can be used as a replacement for the raidtools, or as a supplement. The pos describes a way to assemble a software RAID in rescue mode.
1. Boot into rescue mode.
2. First create the mdadm.conf file with the disks available
# mdadm --examine --scan >> /etc/mdadm.conf
3. Assemble the array
# mdadm --assemble --scan /dev/md0
4. If you do not use LVM, you can stop here and mount the partitions available on the software raid device md0
For example,
# mkdir /test # mount /dev/md0 /test
If you use LVM, please continue at step 5.
5. Scan the lvm devices
# pvscan # vgscan
6. Activate the lvm volumes
# vgchange -ay
7. Similar to step 4., mount the logical volumes
# mkdir /data # mount /dev/mapper/rootvg-lv_root /data