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34 Using Special Features in Libraries
drive while not adding significant processing overhead to the drive or
automation controller.
ACI Commands That Affect Drive Streaming Performance
Commands that alter the state of the drive in some way will affect the
performance of the drive when stream reading or writing. It is recommended
that no command within the following set are sent to the drive while the drive
is writing or reading as it would affect the data throughput to or from the
drive:
3
Load
3
Unload
3
Send Firmware Image
3
Send Firmware Segment
3
Reset
3
Set Drive Configuration—if the Primary Interface (SCSI or FC) is
reconfigured
3
Send SCSI with the following opcodes:
— Mog Select
— Mode Select
— Mode Sense
— Request Sense
— Read Attribute
— Write Attribute
ACI Communications Retry
The ACI specifies a comprehensive packet retry mechanism. Under certain
timing conditions, especially for automation controllers that use a single
microprocessor and multiplex the ACI from one tape drive to another, the
automation controller can receive a response packet from the tape drive that
it does not need. When this situation arises, the automation controller should
send a positive acknowledgement control character, <ACK>, to the tape drive
and discard the packet. Since the tape drive receives the <ACK>, it will not
re-send the packet.