Finally, I got my setup working ok, now if I detach my first harddrive, it boots off second drive.
I followed comment by burke3gd on first page of this howto, and instead running 'update-initramfs -u', I done dpkg-reconfigure mdadm.
Falko, thanks to you a lot for writing such a helpful howto, as well as your continuous support all the times. Thanks to burke3gd also, as I got my setup working by your pointing few things.
Now, there are couple of questions in my mind:
1. During testing as I removed one of the harddrive, the RAID array became degraded. So, after connecting the drive to its place, array will not become complete. Can I make it complete just by
mdadm --add /dev/md0 /dev/sdb1
or I shall need to follow complete process to change failed harddrive as guided in the said howto - step 9 onwards?
2. At present both of my harddrives are of same capacity and model. In future, if any of of drive fails (in real), and if I do not get the new drive of same capacity, shall it work with new higher capacity drive?
Thanks a lot once again.