Quantum DLT 2000, Product Manual

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DLT2000 SCSI Interface
DLT2000/DLT2700 Cartridge Tape Subsystem 8-7
8.2.11 BUS FREE
There are several situations when the device might or will go to BUS FREE
unexpectedly, as defined in the SCSI-2 standard (see sections 6.1.1 and 6.3):
•
An internal hardware or firmware fault that makes it unsafe for the device to
continue operation without a full reset (similar to a power-up reset).
•
ATN asserted or bus parity error detected during non-tape data transfers.
8.2.12 BUS PARITY ERRORS
The occurrence of bus parity errors (i.e. single bit errors) are very serious because they
imply the possibility of undetected double-bit errors on the bus, which most likely
would result in undetected data corruption. On properly configured SCSI buses, parity
errors should be extremely rare. If any are detected, they should be quickly addressed
by improving the configuration of the SCSI bus. A well configured SCSI system in a
normal environment should be virtually free of bus parity errors
Bus parity errors cause the drive to either retry the operation, go to STATUS phase, or
go to bus free and prepare Sense Data (see section 6.1.1 in the SCSI-2 specification).
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 negative impacts on device
performance (the data stream on writes cannot be pipelined as well).