Manually copying MBR from one drive to the other GPT drive and configuring GRUB results in booting failure

Question

I run CentOS 6.4. I have SSD 300GB for system files and RAID10 8TB for storage + backup.

SSD system drive is partitioned as follows: fdisk -l /dev/sdb

Disk /dev/sdb: 300.1 GB, 300069052416 bytes
255 heads, 63 sectors/track, 36481 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xc95ec64f

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1          66      524288   83  Linux       (/boot)
/dev/sdb2              66        8421    67108864   83  Linux       (/)
/dev/sdb3            8421       12598    33554432   83  Linux       (/usr)
/dev/sdb4           12598       36482   191847576    5  Extended
/dev/sdb5           12598       16775    33554432   83  Linux       (/var)
/dev/sdb6           16775       18864    16777216   83  Linux       (/tmp)
/dev/sdb7           18864       35574   134217728   82  Linux swap / Solaris

RAID10 8TB (GPT) is partitioned as follows: parted /dev/sda print

Model: ASR7805 RAID 10 (scsi)
Disk /dev/sda: 7999GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt

Number  Start   End     Size    File system     Name     Flags
 1      8389kB  7399GB  7399GB                  primary             (LUKS)
 2      7399GB  7400GB  510MB   ext4            primary  boot       (/boot)
 3      7400GB  7468GB  68.7GB  ext4            /                   (/)
 4      7468GB  7503GB  34.4GB  ext4            /usr                (/usr)
 5      7503GB  7537GB  34.4GB  ext4            /var                (/var)
 6      7537GB  7554GB  17.2GB  ext3            /tmp                (/tmp)
 7      7554GB  7692GB  137GB   linux-swap(v1)  primary             (swap)
 8      7692GB  7992GB  300GB                   primary             (LUKS)

All I wanted is just to use 300GB of space on my /dev/sda (RAID10) for creating an identical image (backup) of my SSD in case of sudden failure. As you could see above, I have partitioned my RAID10 is just absolutely identical way as my current system SSD. Afterwards, I have created exact images of each partition that I have on my current SSD and extracted them to my RAID10 using dump/restore commands.

All is fully copied and set on my RAID10 just the same way as on my current SSD.

I have obviously edited my backed up fstab (on RAID10 /etc/fstab) using proper UUID for mounting on load.

BUT

Whatever I do I cannot properly load the system, as I restart and choose to load from RAID10. The system just doesn't boot (underscore is continually blinking)!?

I have tried to copy first 446 bite of boot sector (dd if=/tmp/mbrsdb.bak of=/dev/sda bs=446 count=1) from my SSD's MBR to my RAID10's MBR but it didn't work?

Now, as I'm all out of any other options, I would like to ask for your help?

Answer 1

You need to install GRUB properly onto the corresponding disk properly, not only copy of MBR. For GRUB2 it's grub-install