Shutdown the system, have the customer engineer replace the faulty disk, and then boot the system. You can boot the system into either single or multiuser mode, depending on whether you need to provide access to your users while the recovery procedure is being performed. For file systems that have mirror copies on the replaced disk, the file system can be used by the users during recovery. For file systems that didn't have a mirror, and that resided on the replaced disk, you will have to deny access to the users. Do this by unmounting the relevant file systems (they will possibly not be mounted as part of the boot up sequence anyway ).

[Step 2.2]