HP Surestore 80fx Optical Drive and Library SCSI-2 Command Reference - Page 98
DisablePre-fetchTransfer, Length, Minimum, Pre-fetch
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NOTE SCSI-2 Drive Command Set Mode Sense (Group 0) Command (1AH) RCD A Read Cache Disable bit of 1 indicates read ahead is disabled. A RCD bit of 0 indicates read ahead is enabled. 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. Minimum Pre-fetch The Disable Pre-fetch Transfer Length default setting is 64. 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 prefetch size is equal to the READ Transfer Length. This field does not affect the operation of the drive. Maximum Pre-fetch The Minimum Pre-fetch default setting is 1 and cannot be changed. 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 prefetch 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. Chapter 2 2-61 SCSI-2 Drive Commands