In a message dated 12/17/2007 10:07:37 A.M. Central Standard Time, [EMAIL PROTECTED] writes: >When you create your channel programs you will need to make sure that the DEFINE EXTENT ranges do not overlap otherwise IOS will again queue your I/O. IOS always "queues" every I/O, but if different parallel queues are involved, as they are for PAV aliases+base, then the queued I/Os are removed from the queue and started. IOS does not serialize starting the I/O because of extent overlap. The serialization happens inside the control unit's microcode. As long as there is no extent overlap as told to the controller by the DX operands, the controller runs all the I/Os simultaneously. If there is any overlap, then as long as all the I/Os that have previously been started are read-only, the controller runs all of them simultaneouslyu. When the first DX command is received by the controller for a new chain that involves write intent within an extent that overlaps a currently running I/O's extent, the controller will not start that new one until all those previously started that overlap it have finished, and any more new read-only ones that overlap the one with write intent that come into the controller after the one with write intent was received will not be started until the one with write intent ends. Bill Fairchild Franklin, TN
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