If a disk drive is defective, you can replace it with another available disk (and its slices) on the system as documented in How to Replace a Component in a RAID 5 Volume. Alternatively, you can repair/replace the disk, label it, and run the metareplace command with the -e option.
Make sure that you have a current backup of all data and that you have root access.
To enable a failed component in a RAID 5 volume, use one of the following methods:
From the Enhanced Storage tool within the Solaris Management Console, open the Volumes node, then open the RAID 5 volume. Choose the Components pane, then choose the failed component. Click Enable Component and follow the instructions. For more information, see the online help.
Use the following form of the metareplace command:
metareplace -e volume-name component-name
-e specifies to replace the failed component with a component at the same location (perhaps after physically replacing a disk).
volume-name is the name of the volume with a failed component.
component-name specifies the name of the component to replace.
# metareplace -e d20 c2t0d0s2