Optical Drive and Library SCSI-2 Command Reference

SCSI-2 Drive Command Set
Mode Sense (Group 0) Command (1AH)
Chapter 2 2-61
SCSI-2 Drive Commands
RCD A Read Cache Disable bit of 1 indicates read ahead is
disabled.
A RCD bit of 0 indicates read ahead is enabled.
NOTE If WCE and RCD are both set to 1, a CHECK CONDITION status is
returned with the sense key/additional sense code set to ILLEGAL
REQUEST/Invalid Parameter List.
DisablePre-fetchTransfer
Length This field sets the threshold value for pre-fetching data
during reads. If the number of blocks to be read is
greater than this value, no pre-fetching occurs.
The Disable Pre-fetch Transfer Length default setting
is 64.
Minimum
Pre-fetch If this bit is set to 0 by the MODE SELECT command, a
CHECK CONDITION status is returned with the sense
key/additional sense code set to ILLEGAL REQUEST/
Invalid Parameter List. Since the MF bit is 1 and the
Minimum Pre-Fetch bit is also 1, the minimum pre-
fetch size is equal to the READ Transfer Length. This
field does not affect the operation of the drive.
The Minimum Pre-fetch default setting is 1 and cannot
be changed.
Maximum
Pre-fetch If this bit is set to 0 by the MODE SELECT command, a
CHECK CONDITION status is returned with the sense
key/additional sense code set tot ILLEGAL REQUEST/
Invalid Parameter List. Since the MF bit is 1 and the
Maximum Pre-fetch bit is also 1, the maximum pre-
fetch size is equal to the READ Transfer Length. This
field does not affect the operation of the drive.
The Maximum Pre-fetch default setting is 1 and cannot
be changed.