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Chapter 5 SCSI Interface

SCSI Message System

56 Quantum|ATL PowerStor L200 Series Library User’s Guide

Bus Free 5

There are several situations when the device will go to BUS FREE

unexpectedly, as defined in the SCSI-2 standard (see sections 4.1.1

and 4.3):

• 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.

Bus Parity Errors5

Bus parity errors (single bit errors) are very serious. They imply

the possibility of undetected double-bit errors on the bus. Most

likely these result in undetected data corruption. On properly

configured SCSI buses, parity errors are extremely rare. If any are

detected, they should be addressed quickly 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 library to either retry the operation, go

to Status phase, or go to BUS FREE and prepare sense data.

Retrying of parity errors during the data out phase is normally not

done, but can be enabled by changing the EnaParErrRetry

parameter in the Vendor Unique (VU) EEROM mode page. This

feature is disabled by default because of negative impacts on

device performance. Additionally, the data stream on writes

cannot be pipelined.

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Quantum L200 Guía de usuario Pagina 72