Reference Guide

Chapter 4 SCSI Commands
Overview of SCSI Command and Status Processing
DLT-S4 Interface Reference Guide 26
Unit Attention Condition 4 Queued Unit Attentions are implemented on the DLT-S4 tape drive and
are maintained separately for each valid LUN for each initiator. Unit
Attentions are created in each of the following circumstances:
• At power-on.
• When the medium may have changed asynchronously.
• When another initiator changes the
Mode parameters.
• When a firmware (microcode) update has completed.
•Following a
TARGET RESET or LOGICAL UNIT RESET task
management function.
• For Parallel SCSI Only — Change of SCSI bus transceivers (SE or
LVD).
• For Parallel SCSI Only — SCSI Bus Reset
• For Fibre Channel Only — Port logout or implicit logout.
• For Serial Attached SCSI only — Link reset sequence with hard reset.
Up to three Unit Attentions may be queued for each initiator. If an
initiator does not clear its queued Unit Attentions, any additional Unit
Attention conditions are not reported.
Data In/Out Command
Components
4
Many of the SCSI commands cause data to be transferred between the
initiator and the tape drive. The content and characteristics of this data
are command-dependent. Table 13
lists the information transmitted with
each of the commands.
The drive uses the “Length in CDB” column of table 13
to determine how
much command-related data are to be transferred. Table 12
lists how the
units (bytes or logical blocks) for the different Length fields are implied
by the Length field name as follows:
Table 12 Units for Lengths
Fields
Field Name Units Implied
Allocation Length Bytes of data the drive is allowed to send to the
initiator.
Parameter List Length Bytes of data the initiator has available for the drive.
Transfer Length Logical number of data blocks or data bytes the
initiator wants transferred or verified.
Byte Transfer Length Bytes of data the initiator wants transferred.