http://www.seedsofgenius.net/uncategorized/solaris-tips-enable-svm-while-booted-from-alternate-media
This operation is not officially supported, so use it at your own risk.
Often times administrators must boot a Solaris from alternate media in single user mode (failsafe, cd/dvdrom, or network image) in order to make repairs to the installed OS. In this environment, no Solaris Volume Manager (SVM) module is loaded, so if the OS is mirrored it is impossible to work on the installed OS without de-synchronizing the mirrors. Attempting to boot or run Solaris on descynchronized mirrors is extremely unstable and it may cause kernel panics or worse, data corruption.
The supported method for dealing with this is to unencapsulate the root mirror(s), then to boot the system on plain slices before splitting, re-encapsulating, and re-synching the mirrors.
A shortcut to this process is to load the SVM driver and configuration files in the alternate media boot environment:
1) Mount one slice of the root fs
# mount /dev/dsk/c0t0d0s0 /a
2) Copy the configuration
# cp /a/kernel/drv/md.conf /kernel/drv
3) Unmount the root fs
# umount /a
4) Load the SVM module
# update_drv -f md
devfsadm: mkdir failed for /dev 0x1ed: Read-only file system <- expected
5) Mount the metadevice and make necessary changes
# mount /dev/md/dsk/d0 /a
6) Sync the mirrors if necessary
# metasync d0
or
# metasync -r