User`s guide

Chapter 4 SCSI Interface
General SCSI Bus Operation
52 ATL PowerStor L200 Series Library User’s Guide
General SCSI Bus Operation
4
This section discusses general SCSI bus operation.
Note:
DLT tape drive commands are not discussed in this manual. These
commands are described in the SCSI interface chapter of the product
manual for your library drive option.
Data Transfer
4
The L200 supports asynchronous and synchronous data transfers. The
product has both differential and single ended interfaces. Odd parity is
generated during all information transfer phases where the device
writes data to the SCSI bus, and checked during all information
transfer phases where data is read from the bus.
During operations that take significant amounts of time, such as Move
Media commands, the device disconnects from the SCSI bus, allowing
other devices to access the bus. This disconnection is configurable
through the Disconnect-Reconnect Mode Parameters page.
Initiator/Target
Operation
4
The library does not act as an initiator on the SCSI bus. Therefore, the
device will not do any of the following:
•
generate unsolicited interrupts to the host
•
initiate its own SCSI commands
•
assert bus reset
SCSI IDs and Logical
Unit Numbers (LUNs)
4
The library has one logical unit. The library always appears as
LUN 0
.
If the
LUN
specified in the
IDENTIFY
message is invalid, the library
will accept the Command Descriptor Block (CDB). There are three
cases in which this happens:
•
If the command is
INQUIRY,
the target will return the
INQUIRY
data with the peripheral qualifier set to
011
, indicating that the
target will never support the
LUN
in question.
•
If the command is
REQUEST SENSE
, the target will return sense
data. The sense key will be
ILLEGAL REQUEST
, with an
additional sense code of
INVALID Logical Unit Number
.
•
For any other command, the target will terminate the command
with
CHECK CONDITION
status, and generate the Sense Data.