Hitachi HUS151473VL3800 Specifications - Page 259

gets send a Simple message immediately after the Identify message in Message In phase just after Reselection. 2. Each initiator can issue either a tagged command or an untagged command exclusively at the same time. Other initia- tors can exist which operate mutually exclusively with tagged or untagged commands 3. When DQue (Disable queue) of mode page 0Ah is 1, if an initiator issues a tagged command, the drive returns "Mes- sage Reject" message (07h) and receives that command as an untagged command. 4. Queue Tag number does not affect the order of execution. 5. If an initiator issues a command with a queue tag which is the same as the current I/O process or queued I/O process. The target returns Incorrect Initiator connection. 6. A series of linked commands are a single I/O process and are assigned the queue tag established in the initial selection. A command received with a Head-of-Queue tag message shall not suspend a series of linked commands for which the target has begun execution. 7. If DQue is changed to 1 while queued commands exist, all queued commands for the all initiators will be aborted. All future commands received from any initiator with a queue tag will be processed as untagged commands with a message reject message being returned immediately after the qtag is received by the target. 20.4 Command Reordering Command reordering function is supported under tagged command queuing enabled (DQue = 0). The recorder feature reorders Read/Write commands in order to minimize seek time between commands. This function will improve total throughput of the drive. 20.5 Concurrent I/O Process The Concurrent I/O process when multiple I/O processes are active (not queued) on the same logical unit at the same time. The target may start the data phase of an I/O process while another I/O process is not completed. The following I/O processes are allowed to execute concurrently: • Unlinked and untagged Request Sense and Inquiry during execution of other commands. • One of the following commands can be executed while another one or the same one of the following commands is being executed, if those are untagged or Simple tagged commands. - Read(6), Read (10) - Write(6), Write (10) When an I/O process ends in check Condition Status, the drive enters the Contingent Allegiance Condition and other queued I/ O processes from the same initiator will not execute until the CAC is cleared by that initiator. See Section 20.16, "Contingent Allegiance Condition" on page xxx for details. If an I/O process(P-1) encounters an error while another I/O process (P-2) is active, the drive returns check Condition to P-1. If P-2 is from the same initiator as P-1 the drive will suspend P-2 at the earliest convenient point and will not reconnect for data or status. Depending on the setting of QErr bit in the Control mode page, P-2 will either be suspended until the CAC is cleared or terminated. If the drive gets an error on P-2 before suspending the execution of P-2, it will keep the sense data separately from the sense data for P-1. The sense data for P-2 will be set after the Contingent Allegiance condition caused by P-1 is cleared. If P-2 is from a different initiator than P-1, then P-2 is allowed to continue executing after entering CAC for P-1, pending QErr is not set to terminate all processes to all initiators. Then if an error occurs on P-2 before the CAC is cleared on P-1, the drive will send check condition and generate a CAC for P-2 while maintaining the CAC and sense for P-1. 20.6 Write Cache If the WCE (Write cache enable) bit is 1, the drive returns Good Status and Task complete message and goes to Bus Free immediately after receiving the data of the last sector before actually writing the data onto the media. If the drive detects an error after it returns a Good Status, the drive sets a Deferred Error (Error Code of sense data = 71h) and a following command will be returned with Check Condition and the Contingent allegiance condition is established. Under the Hitachi Ultrastar 15K147 SCSI Hard Disk Drive Specification 241