User's Guide

Chapter 3 Emulated DLT7000 SCSI Commands
Mode Select (6 /10) (15h / 55h)
Quantum DX-Series Software Interface Guide 177
Table 132 MODE
SELECT Mode
Parameter Header -
Field Descriptions
Field Name Description
Media Type This field is ignored by the MODE SELECT
command.
Buffered
Mode
Default = 1. The drive implements immediate
reporting on WRITE commands through its
buffered mode. With Buffered Mode set to 1, the
drive reports GOOD status on WRITE commands as
soon as the data block has been transferred to the
buffer. If this field = 0, then the drive does not
report GOOD status on WRITE commands until the
data blocks have been written to tape.
When Buffered Mode is not used, the tape drive
suffers significant performance degradation, and
possible capacity, depending on tape format, block
size, and compression. When writing 2.6 or 6.0 GB
formats and block size that is a multiple of 4 Kbytes,
there is no capacity loss. Likewise, when using the
10 or 20 GB format with compression disabled and
block size a multiple of 8 Kbytes, there is no
capacity loss.
When writing 10 or 20 GB format with compression
enabled and Buffered Mode disabled, some
capacity loss can occur. The block packing feature is
essentially disabled by turning off Buffered Mode.
If Buffered Mode is set to a number greater than 1,
the command is rejected with CHECK
CONDITION, sense key of ILLEGAL REQUEST.
Speed The tape drive supports only its default speed.
Block
Descriptor
Length
This field specifies the length in bytes of all the
block descriptors. Since the drive only allows one
block description, the value must be either 0 or 8. A
value of 0 indicates no block description is included;
a value of 8 indicates a block descriptor is present
and precedes the mode page data. Any other value
other than 0 or 8 causes a CHECK CONDITION
status with sense key of ILLEGAL REQUEST to be
returned.