IBM Enterprise Server H80 Series - Manual (Page 162)

Spare Sector Availability
This selection checks the number of spare sectors available on the optical disk. The
spare sectors are used to reassign when defective sectors are encountered during
normal usage or during a format and certify operation. Low availability of spare
sectors indicates that the disk needs to be backed up and replaced. Formatting the
disk does not improve the availability of spare sectors.
You can run this task directly from the AIX command line. The following usage
statement describes the syntax of the command:
diag -c -d deviceName -T chkspares
146 RS/6000 Enterprise Server Model H80 Series User's Guide