A buddy sent this to me years ago when we both had a bunch of IRIX systems to admin.  It works for most *nix platforms with only minor adjustments.  The point of this process is to clone a working drive without mirroring.  Mirroring is a great lazy method for protecting against drive failure, but doesn't help at all when our users "opps I deleted something really important" or a patch corrupts the kernel.

Keep in mind that you will need to repeat this process after every new install, update, or upgrade (assuming it worked) and it's best to have yet another drive or remote storage for data when working like this.

WARNING: Make sure the data you want to copy does not exceed the disk capacity of your second disk drive.

1. Assumes two separate drives - the first contains the OS and data - the second is empty.

2. Boot the machine in single user mode. While booting, stop at the Command Monitor and type ‘single’.

3. In single user mode:

fx -x to partition the drive in root drive.

4. Create a file system on the second disk:
mkfs /dev/rdsk/dks0d2s0

5. Check the integrity of the disk:
xfs_check /dev/rdsk/dks0d2s0

6. Mount the second disk on a mount point:
mkdir /disk2

mount /dev/dsk/dks0d2s0 /disk2

7. Check if the mount point it's there:
df -k

8. Set the name on the host machine:
uname -S "Your machine name"

9. Copy all the data on disk 1 to disk2:
xfsdump -J - / | xfsrestore - /disk2

Note: If xfsdump is interrupted <ctrl+c>, the content of the destination directory must be deleted, otherwise, you won't be able to relaunch step 9.

10. When completed, unmount disk2
umount /disk2

11.Go to /usr/tmp directory:
cd /usr/tmp

12. Copy the sash in the volume header on the fist disk:
dvhtool -v get sash sash /dev/rdsk/dks0d1vh

13. Just in case try to delete the one on the seconds disk:
dvhtool -v del sash /dev/rdsk/dks0d2vh

14. Copy the sash to the seconds disk:
dvhtool -v add sash sash /dev/rdsk/dks0d2vh

15. Verify all disk have a sash in the volume header:
dvhtool -v list /dev/rdsk/dks0d1vh

dvhtool -v list /dev/rdsk/dks0d2vh

16. If it looks good shutdown and reboot with the first disk disconnected.

17. If it boots - great!  If not, reconnect the original drive and start over.