Update the Boot Archive on a RAID 1 Volume

Check the current meta devices and mirror status before reboot
metastat -p
like d0 d10 d20

Go to fail safe mode:
ok boot -F failsafe or reboot -- "-F failsafe"

Mount primary submirror
mount /dev/dsk/c0t0d0s0 /a

Update vfstab
backup original cp /a/etc/vfstab /a/etc/vfstab.orig

Comment out / filesystem
#/dev/md/dsk/d0     /dev/md/rdsk/d10    /     ufs    1    no    -

Add sub-mirror disk as /
/dev/dsk/c0t0d0s0 /dev/rdsk/c0t0d0s0  /     ufs    1    no    -

Update system conf
Backup original cp /a/etc/system /a/etc/system.orig

Comment out rootdev
* Begin MDD root info (do not edit)
# rootdev:/pseudo/md@0:0,0,blk
* End MDD root info (do not edit)

Update boot archive
bootadm update-archive -R /a

Reboot
umount /a
shutdown -i 6

Detach faulty sub-mirror
metadetach d0 d20

Replace changed file
cp /etc/vfstab.orig /etc/vfstab
cp /etc/system.orig /etc/system

Reboot
shutdown -i 6

Attach sub-mirror
metattach d0 d20

Check resync
metastat