Seagate Scorpion 240 DDS-4 Installation Manual page 52

A-50 Scorpion 240 Autoloader Installation Manual
If this error is encountered, make sure that the correct
modifications were made to the file /var/sysgen/master.d/scsi.
Switching Hardware Compression
Irix 6.x provides support for software switching of hardware
compression through the use of different device drivers.
Drivers including a "c" in the device name should enable
compression. You may be able to resolve problems with data
compression by installing the latest Irix 6.x patch set.