Quantum LTO 2 User Manual page 47

Chapter 1 SCSI Interface
General Behaviors
1
LUN 1 Command Forwarding
A tape library or autoloader containing a LTO can receive its SCSI
commands via the LTO drive. This function is called "Command
Forwarding" and is enabled via the "CmdFwd" field in the Interface
Control mode page (22h). When enabled, commands received via the
SCSI bus and addressed to LUN 1 are immediately transmitted to the
library via the RS-422 interface. LTO acts as a bridge, passing commands,
data, and status between the initiator and the library, as specified in the
Library Interface Encapsulated SCSI Protocol Manual.
In SCSI Medium Changer terminology, the library or autoloader appears
as an "independent medium changer," because the tape drive and
medium changer are at different LUNs. Medium changer commands
addressed to LUN 0 are rejected with Check Condition and sense data of
Illegal Request / Invalid Command Operation Code (05/20/00).
In the Parallel SCSI drive, because of the relatively slow communication
on the RS-422 interface, LTO will disconnect from the SCSI bus after
receiving a command, after receiving data-out, and after sending status.
Data-in and status are sent to the initiator without disconnecting between
them.
If the link fails between the LTO and the library, the failed command will
receive a status of Check Condition and sense data of Aborted Command
/ Logical Unit Communication Failure (0B/08/00).
If a SCSI bus reset or a Target Reset task management request is received,
then either a Target Reset or Logical Unit Reset task management request
is transmitted to the library. The library must be capable of processing
either request.
When command forwarding is disabled in mode page 22h, commands
addressed to LUN 1 will receive a status of Check Condition and sense
data of Illegal Request / Logical Unit Not Supported (05/25/00).
After Command Forwarding is enabled or disabled, the drive will
respond to the next command with a Check Condition and sense data of
Unit Attention / Reported LUNs Data Has Changed (06/3F/0E).
LTO-2 SCSI Interface Guide 23