HP StorageWorks DLT80, Reference Manual

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Overview
17 DLT80 Tape Drive Reference Guide
Data Compression
The DLT80 drive reads and writes both uncompressed (native) and Digital
Lempel-Div (DLZ) compressed data. The DLT80 drive features a native formatted
capacity of 40 GB and a sustained native data transfer of 6.0 MB/s.
When operating in compressed mode, data capacity is affected by how much the
data can be compressed. Most data can be compressed at an approximate 2:1 ratio.
This would provide the DLT80 drive with a compressed capacity of 80 GB and a
compressed data transfer up to 12 MB/s.
The DLT80 drive ships from the factory with data compression enabled for
writing. In this mode, data is always compressed when writing to the tape, but the
drive is capable of reading both compressed and uncompressed tapes. For the
drive to write uncompressed data, the data compression setting must be changed
through the software. To change it, consult the backup application software
documentation for the data compression enabling and disabling procedure.
Using the Density Select button on the front panel can also disable/enable data
compression but is only effective per session. See "Front Panel LEDs and
Buttons" in Chapter 5 for more information.
Note: Capacity may vary based upon actual stored data. Data transfer rate can vary
depending on actual data.