Reference Guide

Chapter 4 SCSI Commands

Overview of SCSI Command and Status Processing

DLT-S4 Interface Reference Guide 30

• Serial Attached SCSI

• Transceivers are turned on, auto speed negotiation occurs, and

the link reset sequence is initiated.

• The drive rewinds the tape to Beginning of Tape (BOT).

• The drives goes through a calibration process at power-on and

loading of media.

• Following power-on self test (POST) and self initialization, the

tape drive is ready to respond to interface traffic. The drive

responds to tape motion commands with

CHECK CONDITION

status, Sense Key set to

NOT READY, until the tape medium is

ready.

Data Cache and Tape

Write Interaction

The DLT-S4 tape drive contains a data cache that buffers blocks and

filemarks until it writes them to tape. This section describes what

happens when the drive writes, or “flushes,” those blocks to tape. A

MODE SELECT parameter allows the data cache to be disabled

(unbuffered mode). In this mode, every

WRITE command causes data to

be written to the tape medium before the drive returns the message to the

host.

The DLT-S4 tape drive writes the contents of the write data cache to the

tape medium under the following circumstances:

• When the initiator issues a

WRITE FILEMARKS command with the

Immediate bit set to 0.

• When data has been in the cache longer than the maximum time

specified by the value of the

MODE SELECT command Write Delay

Time parameter (the default is 10 seconds).

• When the drive receives a non-write-type media access command.

• When a

RESET condition occurs.

Note: Unbuffered mode is NOT recommended due to the poor

performance that may result.