User's Manual

Theory of operations

Refer to Chapter 4 for information about loading new firmware using a Seagate

firmware upgrade cartridge.

Sensors

A number of mechanical and optical sensors are integrated in the drive design. The

cartridge in

and

cartridge loading

sensors are mechanical sensors that determine the

position of the loading mechanism. The other mechanical sensors report specific

information based on detecting the open or closed state of four recognition holes in

the DAT cartridge. The open or closed state of these holes designates tape type, that

is, whether the tape is a cleaning cartridge, whether the tape is prerecorded and

whether the tape cartridge is write-protected. These mechanical sensors and the

sensor for the cartridge in status comply with the DDS standard requirements for the

cartridge.

The beginning-of-tape (BOT) sensor is an optical sensor that uses the light path

transmissivity of leader tape, as specified in the DDS cartridge standards. The

sensor is also designed to recognize media recognition system (MRS) cartridges,

which have a series of alternate opaque and clear stripes at the beginning of the

tape.

The reel sensors for the two reels are optical. Optical sensors also detect the

mechanism position during mode changes.

The capstan sensor is a magnetoresistive Hall sensor that detects a magnetic field.

The cylinder sensors are coil and magnet sensors. Each reel motor contains a high-

resolution, optical-speed encoder.

Read-After-Write

The read-after-write (RAW) technique provides a means of verifying that host data

was written on the tape correctly by applying a read check immediately after writing

the data to tape. The read check is a comparison of the actual signal quality versus a

predetermined acceptable threshold level.

If a frame is identified as bad, it is rewritten later down the tape. The bad frame is not

necessarily rewritten immediately. It can be rewritten after three, four or five other

frames have been written. Any frame can be rewritten multiple times to provide for

skipping over bad areas on the tape.

Excessive consecutive rewrites typically signal a degraded media condition; in these

cases it is best to discontinue use of the tape in question and to 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 operations, and of the reduced threshold during

read operations, ensures that data is written with the highest possible margin and

that recorded data can be read or retrieved with the highest possible confidence.