Quantum DLT 8000 Manual descargar pdf (Pagina 114)

SCSI Description

3-12 Quantum DLT 8000 Tape System

CAUTION

Any occurrence of a bus parity error (i.e., a single-bit error) should be considered

serious: it implies the possibility of undetected double-bit error may exist on the bus.

This may cause undetected data corruption. On properly configured SCSI buses, parity

errors are extremely rare. If any are detected they should be addressed by improving

the configuration of the SCSI bus. A well-configured SCSI bus in a normal environment

should be virtually free of bus parity errors.

Bus parity errors cause the tape drive to retry the operation, go to the STATUS phase, or

go to BUS FREE and prepare Sense Data. Retrying of parity errors during Data Out

Phase when writing is normally not done, but can be enabled by changing the

EnaParErrRetry parameter in the VU EEROM Mode Page. This feature is not enabled by

default because of possible negative impact on device performance (the data stream

on writes cannot be pipelined as well).

Initiators normally do not expect the BUS FREE phase to begin because of the drive’s

release of the BSY signal unless it has occurred after the detection of a reset condition or

after a drive has successfully transmitted or received one of the following messages:

Messages Transmitted from Drive:

• DISCONNECT

• COMMAND COMPLETE

Messages Received by Drive:

• ABORT

• BUS DEVICE RESET

• RELEASE RECOVERY

• ABORT TAG

• CLEAR QUEUE

If an initiator detects the release of the BSY signal by the drive at any other time, the

drive is indicating an error condition to the initiator. The drive can perform this

transition to the BUS FREE phase independently of the state of the ATN signal. The

initiator manages this condition as an unsuccessful I/O process termination. The drive

terminates the I/O process by clearing all pending data and status information for the

affected nexus. The drive can optionally prepare sense data that can be retrieved by a

REQUEST SENSE command.

Bus Free Sequence

1. BSY and SEL signals are continuously false for one bus settle delay.

2. SCSI devices release all SCSI bus signals within one bus clear delay.

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Quantum DLT 8000 Manual Pagina 114