When using Drive Setup to perform an extended operation, such as testing the disk, initializing the disk with a low level format, or zeroing all data, use the Energy Saver control panel to set the hard drive sleep setting to "Never".
This prevents errors caused by the hard disk spinning down before Drive Setup completes the operation.
If you have experienced other difficulties since installing Mac OS 8.5 please read the About Mac OS 8.5 Read Me and Installing Mac OS 8.5 Read Me that come with Mac OS 8.5.
This information is from Knowledge Base article 58129: "
Mac OS 8.5: About Mac 0S 8.5 Read Me".