My storage server ( NAS box) consists of 4 drives and each with 4 partitions, so total 16 drives. I have made the following RAIDS
RAID0 from sda4 and sdb 4 for /boot.
Raid 5 from sda3, sdb3,sdc3 and sdd3 for /
Raid 5 from sda2, sdb2, sdc2 and sdd2 for /data
Raid 0 from sdc1 and sdd1 for properetary inforamation.

The OS is able to boot from sda4 successfully. I have removed sda4 and tried to the machine from sdb4 and this is not functioning. I did
grub> find /boot/grub/stage1

I swapped the positions of sda and sdb, even after that Os is not booting from sdb which is in first position of the physical drive order in NAS box.

Appreciate some one's help.

Ashok Nalla