Quantum DLT1/VS80 SCSI, Interface Manual

Page: 30 / 182

Chapter 2: General SCSI Bus Operation
2-6 July 2004 81-81276-01 Rev A01
These commands do not require access to the data cartridge:
•
INQUIRY
•
LOG SENSE/SELECT
• MODE SELECT
•
MODE SENSE
•
PREVENT/ALLOW MEDIUM REMOVAL
•
READ BLOCK LIMITS
•
READ BUFFER
•
READ ELEMENT STATUS
•
RECEIVE DIAGNOSTIC RESULTS
•
REQUEST SENSE
•
RESERVE/RELEASE UNIT
•
SEND DIAGNOSTIC (non-media access diagnostics)
• WRITE BUFFER.
N
OTE
: The TEST UNIT READY command determines whether the tape drive
would accept a data cartridge access command without returning CHECK
CONDITION status.
2.8.3 BUS FREE Phase
Some situations can cause the tape drive to go to BUS FREE unexpectedly, as defined in the SCSI-2
standard (see sections 6.1.1 and 6.31 in the SCSI-2 specification):
•
An internal hardware or firmware fault that makes it unsafe for the tape drive to continue operation
without a full reset (similar to a power-up reset)
•
Bus parity error detected during non-medium data transfers.
2.9 Bus Parity Errors
The occurrences of bus parity errors (that is, single bit errors) are very serious because they imply the
possibility of undetected double-bit errors on the bus. These most likely would result in undetected
data corruption. On properly configured SCSI buses, parity errors should be extremely rare. If bus
parity errors are detected, they should be quickly addressed by improving the electrical and mechanical
configuration of the SCSI bus.
A well-configured SCSI system bus in most normal environments should be practically free of bus
parity errors.