User's Guide

Chapter 2 Installing Internal Tape Drives
Data Compression
DDS-4/DAT 72 User’s Guide 19
Data Compression 2
Settings:
Switch 1 ON = Enable hardware data compression (default)
Switch 1 OFF = Disable hardware data compression
Switch 2 ON = Recognize SCSI data compression commands (default)
Switch 2 OFF = Ignore SCSI data compression commands
The internal tape drive provides two switches for controlling data
compression.
Switch 1 determines whether hardware data compression is enabled or
disabled. By default, switch 1 is set to ON, enabling hardware data
compression. To disable hardware data compression, set switch 1 to the
OFF position.
Switch 2 controls whether SCSI commands are recognized for enabling or
disabling hardware data compression. By default, switch 2 is set to ON,
allowing SCSI commands to be used to enable or disable hardware data
compression. To prevent SCSI commands from enabling or disabling
hardware data compression, set switch 2 to the OFF position.
When data compression is enabled, the drive compresses all data written
to tape and decompresses all compressed data read from tape. The degree
of compression varies due to the type of data being processed.
• Data with a high degree of redundancy, such as structured database
files or graphics files, are compressed most efficiently, often at a ratio
of 2:1 or more.
• Data with little redundancy, such as executable programs, are
compressed the least.