IBM Ultrastar 36LZX Specifications page 106

Target will transfer 1 block of data before attempting to disconnect. Value of 0000h indicates there is
no limit on the amount of data transferred per connection. Regardless of the value in Maximum Burst
Size the Target disconnects prior to completion of the data phase if the internal data buffer segment
becomes empty during a Read command or full during a Write command.
Ÿ DIMM (Disconnect Immediate) bit allows the Initiator to determine whether the Target is required to
disconnect after the receipt of a command and prior to starting a data phase. When the DIMM is set
to 1, the Target disconnects from the SCSI Bus after the receipt of a command and prior to starting a
Data In or Data Out phase.
Note: Priority commands do not disconnect from the SCSI bus.
For Write (6), Write (10), Write and Verify, and Write Same commands (opcodes 0Ah, 2Ah, 2Eh,
41h), DIMM set to 0 indicates that the Target is not allowed to disconnect from the SCSI bus after
receiving the command and prior to starting the Data Out phase unless the write command must be
queued. The Target remains connected to the SCSI bus until the Data Out phase is started. After the
Data Out phase is started, the Target may disconnect to free the SCSI bus for use by other devices.
For Read (6) and Read (10) commands, DIMM set to 0 prevents the Target from disconnecting from
the SCSI Bus until it has determined that the requested data is not available in the data buffer. If the
data is available, the Target will not disconnect prior to starting the data transfer unless the read
command must be queued. If the data is not available, the Target disconnects until enough data has
been read from the disk to satisfy the reconnection criteria as determined by the Read Buffer Full
Ratio.
All other commands with DIMM set to 0 may or may not disconnect before a data phase is started.
Note: Disconnection is based on the Target's internal control algorithms, the setting of the discon-
nect privilege bit in the previous Identify message, and other parameters in this mode page.
Ÿ DTDC (Data Transfer Disconnect Control) field defines further restrictions for when a disconnect is
permitted.
- A value of 00b indicates that DTDC is not used by the Target and the disconnect is controlled by
the other fields in this page.
- A value of 01b indicates that the target shall not attempt to disconnect once the data transfer of a
command has started until all data which the command is to transfer has been transferred. The
connect time limit and bus inactivity limit are ignored during the data transfer.
- The value 10b is reserved.
- A value of 11b indicates that the target shall not attempt to disconnect once the data transfer of a
command has started until the command is complete. The connect time limit and bus inactivity
limit are ignored once data transfer has started.
Note: If DTDC is nonzero and the maximum burst size is nonzero, a CHECK CONDITION status will
be returned. The sense key shall be set to ILLEGAL REQUEST and the additional sense code set to
ILLEGAL FIELD IN PARAMETER LIST.
Ÿ Fair arbitration If the Fair arbitration filed is set to 000b, the target shall not use arbitration fairness
during normal arbitration. If this field is set to a nonzero value, the target shall use arbitration
fairness during normal arbitration.
Both the Read Buffer Full Ratio and the Write Buffer Empty Ratio pertain to the current active notch. For
each active notch as defined in page 0Ch there are separate Read Buffer Full Ratios and Write Buffer
Empty Ratios. When the active notch is set to zero, the values are applied in mode page 0Ch across all
notches.
Ultrastar 36LZX hard disk drive specifications
106