Shutdown the system, have the customer engineer replace the faulty disk, and then boot the system in single user mode from the alternate boot disk. If you only have two disks in the root volume group, then you will need to override quorum as you boot. Note that you don't have to boot in single-user mode if all of the disk's data is mirrored elsewhere (but you may still have to override quorum).

For our example:

        ISL> hpux -is (52.5.0;0)/stand/vmunix

  OR

        ISL> hpux -is -lq (52.5.0;0)/stand/vmunix
        (if you need to override quorum.)

[Step 4.2]