mceith.com

Most common tools for handling linux software RAID would be mdadm and raidtools.

Check raidstatus:

# cat /proc/mdstat 

Personalities : [linear] [raid0] [raid1] [raid5] [multipath] [raid6] [raid10] [faulty] 
md1 : active raid1 hdb2[1] hda2[0]
      38073984 blocks [2/2] [UU]
      
md0 : active raid1 hdb1[1] hda1[0]
      1003904 blocks [2/2] [UU]

I am too lazy to show what it will show when broken, you will know when you see it. Also check dmesg for errors.

So after reboot if you have identical disk you can just copy partition table:

sfdisk -d /dev/hda | sed s/hda/hdb/ > /tmp/hdb
sfdisk -f /dev/hdb < /tmp/hdb

I think that everyone can figure out what just happened. No add the fresh disk to degraded array:

raidtools

raidhotadd /dev/md0 /dev/hdb1
raidhotadd /dev/md1 /dev/hdb2

mdadm

mdadm /dev/md0 -a /dev/hdb1
mdadm /dev/md1 -a /dev/hdb2

After that if the reconstruction speed is low, you can speed it up by raising the speed_limit_min under /proc/sys/dev/raid

 echo 10000 > /proc/sys/dev/raid/speed_limit_min