HP Surestore 125ex Optical Drive and Library SCSI-2 Command Reference - Page 75
Disable Pre-fetch, Transfer, Length, Minimum, Pre-fetch, Ceiling
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SCSI-2 Drive Command Set Mode Select Command (15H) MF The Multiplication Factor bit is set to 1 and cannot be changed. This bit is used with the Minimum and Maximum Pre-fetch fields during READ operations. 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. Disable Pre-fetch Transfer 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 default value 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 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. Maximum Pre-fetch The default value 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 to 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. Maximum Pre-fetch Ceiling The Maximum Pre-fetch Ceiling field does not affect the operation of the drive and can be set to 32 or 64. If another value is set, a CHECK CONDITION status is returned with the Sense Key/Additional Sense Code set to Illegal Request/Invalid Parameter List. 2-38 Chapter 2