User's Manual

40 Scorpion 240 Product Manual
Excessive consecutive rewrites typically signal a degraded media condition; in these
cases it is best to discontinue use of the tape in question and continue with a new
tape.
During a read or restore operation, the threshold level is reduced to maximize the
likelihood that data can be successfully retrieved from tape. The combination of the
elevated read threshold during write and reduced threshold during read ensures that
data is written with the highest possible margin and that recorded data can be read
or retrieved with the highest possible confidence.
Media Recognition System (MRS)
The Scorpion 240 tape drive includes support for the media recognition system
(MRS), which is unique to DDS products.
The MRS refers to a series of alternate opaque and clear stripes at the beginning of
each tape. These stripes are used to classify the media as data or computer grade,
rather than audio grade media.
Internal to the drive is a system of optical sensors and electronics to identify the MRS
stripes to determine whether the tape is computer-grade media. The MRS capability
can be enabled or disabled using the drive’s dip switch. When enabled, the drive
does not allow any write operations to non-MRS tape cartridges.
All DDS-4 (150 meter), DDS-3 (125 meter), DDS-2 (120 meter) and DDS (90 meter)
tape cartridges have MRS striping to signal that they are computer grade media.
All DDS tape cartridges with the MRS striping either have the MRS logo, the MRS
acronym or
media recognition system printed on them to readily distinguish them
from audio-grade media.
Audio-grade media is not suitable for data or computer backup purposes. It is not
recommended for use in the Scorpion 240 tape drive.
Data compression
Typical data streams of text, graphics, software code or other forms of data contain
repeated information of some sort, whether it is at the text level where you can
readily recognize regular repetitions of a single word or at the binary level where the
repetitions are in bits or bytes. Although most data is unique and random, the binary
level data exhibits patterns of various sizes that repeat with varying degrees of
regularity.
Storage efficiency is increased if the redundancies or repetitions in the data are
removed before the data is recorded to tape. Data compression technology functions
to significantly reduce or eliminate the redundancies in data before recording the
information to tape. This increases the amount of data that can be stored on a finite
medium and increases the overall storage efficiency of the system.
With data compression, the redundant information in a data stream is identified and
then represented by codewords or symbols, which allow the same data to be
recorded in a fewer number of bits. These symbols or codewords point back to the