The /var/adm directory structure is notorious for accumulating large log files and other large files that are useful for debugging problems, but which otherwise use up a tremendous amount of space. The /var/adm/crash directory may be storing several images of the IRIX kernel (from past system failures) and copies of the entire core memory (vmcore). These files can take up large amounts of space (many megabytes) and should be archived on tape and removed from your system.
If you have system auditing enabled, be aware that this facility generates very large audit trail record files, and these will need to be archived to tape on a regular (perhaps daily) basis.
Also, check any UUCP or ftp directories you may have available, and generally look for core files, and any other large and unnecessary files that may exist on your system.