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
4
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.
