Add c7t1d0 to an existing root pool named "rpool" created using the OpenIndiana installer on c7t0d0.

gistfile1.txt

# Add a default partition map on the new drive.
fdisk -B c7t1d0p0

# Copy the disk label from the first disk to the second:
prtvtoc /dev/rdsk/c7t0d0s0 | fmthard -s - /dev/rdsk/c7t1d0s0

# Attach the second disk to the root pool:
zpool attach rpool c7t0d0s0 c7t1d0s0
# You will get an error about overlapping. If you get another error, stop. Otherwise:
zpool attach -f rpool c7t0d0s0 c7t1d0s0

# Check that the disk is resilvering, and wait until it's done.
zpool status rpool

# Install grub on the second disk so it's bootable.
installgrub /boot/grub/stage1 /boot/grub/stage2 /dev/rdsk/c7t1d0s0