User`s guide

Chapter 2 Installing Internal Tape Drives
Reviewing Drive Default Settings
18 DDS-4/DAT 72 User’s Guide
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.
Media Recognition
System (DDS-4
Drives Only)
2
Settings:
Switch 3 ON = Enable MRS (default)
Switch 3 OFF = Disable MRS
Using non-DDS media may appear to give satisfactory results, but the
inferior specifications of such media can cause data-integrity problems.
To avoid these problems, the internal tape drive provides a media-
recognition system (MRS) feature that determines whether tape
cartridges conform to the DDS tape standard.
By default, switch 3 is set to ON, enabling MRS. With this setting, the
drive:
• Reads from and writes to MRS media.
• Reads from but does not write to non-MRS media.
To disable MRS, set switch 3 to the OFF position. With this setting, the
drive reads from and writes to MRS and non-MRS media.
Power-On Self-
Test
2
Settings:
Switch 4 ON = Drive performs Power-On Self-Test (default)
Switch 4 OFF = Drive does not perform Power-On Self-Test
Note: Switch 3 is reserved on internal DAT 72 drives.