Duplicating disks in FreeBSD

Tonight I installed a new system disk in the main feep.org server, in response to these ominous warnings:

(da0:sym0:0:0:0): WRITE(10). CDB: 2a 0 0 30 1 1f 0 0 20 0
(da0:sym0:0:0:0): CAM Status: SCSI Status Error
(da0:sym0:0:0:0): SCSI Status: Check Condition
(da0:sym0:0:0:0): Deferred Error: HARDWARE FAILURE asc:19,0
(da0:sym0:0:0:0): Defect list error field replaceable unit: 2
(da0:sym0:0:0:0): Retrying Command (per Sense Data)

The spare disk was already in the server (it was being used for staging backups, but I moved that elsewhere for now), and was identical to the failing one. So all I really needed to do was duplicate the boot block, partition table, disk label, and filesystems. I was able to do most of this while the system was running normally, which kept downtime to a minimum. In the examples, da0 is the failing disk, and da1 is the new target disk.

First, initialize the disk by creating a DOS partition table (mine already had one):

fdisk -I /dev/da1

Install the boot block:

fdisk -b /boot/mbr

Duplicate the disklabel:

disklabel da0s1 | disklabel -R da1s1 -

Create file systems:

newfs /dev/da1s1a
newfs -U /dev/da1s1e
newfs -U /dev/da1s1f
newfs -U /dev/da1s1d

Copy data:

mount /dev/da1s1a /mnt
cd / && tar -cf - --one-file-system --exclude /mnt . \
   | ( cd /mnt && tar -xpf )
umount /mnt
mount /dev/da1s1e /mnt
cd /tmp && tar -cf - . | ( cd /mnt && tar -xpf )
umount /mnt
mount /dev/da1s1f /mnt
cd /usr && tar -cf - . | ( cd /mnt && tar -xpf )
umount /mnt
mount /dev/da1s1d /mnt
cd /var && tar -cf - . | ( cd /mnt && tar -xpf )
umount /mnt

Now I intended to boot into single-user mode to finish with a final rsync on a very quiet system, but I couldn't boot from da0 any longer; it seemed to be getting worse. So I booted from FreeBSD 5.5 Disc 1 and used the Live CD feature to finish up with a few rsyncs (using the rsync binary from da1, since the Live CD doesn't include it).

mkdir /da0 /da1
cd /da0 && mkdir root tmp usr var
cd /da1 && mkdir root tmp usr var
mount /dev/da0s1a /da0/root
mount /dev/da1s1a /da1/root
mount /dev/da0s1e /da0/tmp
mount /dev/da1s1e /da1/tmp
mount /dev/da0s1f /da0/usr
mount /dev/da1s1f /da1/usr
mount /dev/da0s1d /da0/var
mount /dev/da1s1d /da1/var
/da1/usr/local/rsync -avx /da0/root/ /da1/root
/da1/usr/local/rsync -avx /da0/tmp/ /da1/tmp
/da1/usr/local/rsync -avx /da0/usr/ /da1/usr
/da1/usr/local/rsync -avx /da0/var/ /da1/var
umount /dev/da0s1a
umount /dev/da1s1a
umount /dev/da0s1e
umount /dev/da1s1e
umount /dev/da0s1f
umount /dev/da1s1f
umount /dev/da0s1d
umount /dev/da1s1d

That done, I yanked da0, put da1 in its place, and a fresh disk in da1's place. Everything came up with no problems.