Overview of the DAT Drive
1-5
Compaq Confidential – Need to Know Required
Writer: Debbie McRill Project: Compaq DAT Drive Reference Guide Comments:
Part Number: 155452-002 File Name: Chapter 1 Overview.doc Last Saved On: 3/14/00 5:01 PM
the beginning of the cassette. The drive can be configured to treat non-MRS
cassettes as write-protected. In other words, the drive will only be allowed to
read non-MRS cassettes, not write to them.
Life Expectancy of Cassettes
All DDS-certified media are designed to withstand at least 2,000 passes.
Under optimum environmental conditions (50 percent relative humidity,
22
°
C), this is equivalent to about 100 to 150 backup operations. This takes into
account that an area of cassette may have several passes during a backup,
either because streaming (the optimum performance rate where data is sent to
the drive at approximately the same speed as it is written to the cassette media)
cannot be maintained, or the backup software package repeatedly accesses
certain areas of cassette.
Certain extreme conditions reduce the recommended maximum number of
backup operations. These conditions are as follows:
■
Environmental conditions
Sustained use at the low end of the humidity specification will reduce
the cassette life.
■
Computer performance
The lower the performance of the computer, the more likely that
streaming cannot be maintained and that an increase in the number of
passes over given areas of a cassette will occur.
■
Backup Software
The backup software may access certain areas of the cassette frequently,
or there may be a high system overhead that may cause streaming to
stop. Both of these factors increase the number of cassette passes in a
given area.
Data Compression
The Compaq DAT drive ships from the factory with data compression enabled
for writing. The drive is equipped with onboard DDS-DC hardware, using the
Data Compression Lempel Ziv (DCLZ) algorithm. In this mode, data is always
compressed when writing to the cassette, but the drive is capable of reading
both compressed and uncompressed cassettes. For the drive to write
uncompressed data, you must change the data compression setting.
