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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: iSCSI:Request/Response OrderingThe simple answer is that an initiator may not make any assumptions about the order of requests to the same blocks (by itself or other initiators) that may be outstanding at the same time. If you care about ordering, an initiator must wait until previous requests are complete before issuing a request that references the same block(s). This assumes that all commands are issued as simple tasks, which is the most common situation today (one suspects the only situation). People have suggested more complex schemes in the past, amounting to exporting some portion of the transfer dependency graph to the target. The ordered task attribute is one approach to this. None have proved practical in practice. In practice, if a target receives references to the same block from multiple initiators, it can perform the operations in whatever order it wishes. There is no "correct" order, all are equally valid. (Again, I'm assuming all are issued as simple tasks). Edward A. Gardner eag@ophidian.com Ophidian Designs 719 593-8866 voice 1262 Hofstead Terrace 719 593-8989 fax Colorado Springs, CO 80907 719 210-7200 cell -----Original Message----- From: Sanjeev Bhagat (TRIPACE/Zoetermeer) <iscsi_t10@sanjeevbhagat.com> To: 'IPS Reflector' <ips@ece.cmu.edu>; T10@t10.org <T10@t10.org> Date: Saturday, September 29, 2001 7:03 PM Subject: iSCSI:Request/Response Ordering Hello All (T10, IPS), The SAM-2 specifications makes no assumption about, or places any requirement on the ordering of requests or responses between tasks or task management functions received from different SCSI initiator ports. In this scenario how can a SCSI target make correctly handle the read/write requests made on same blocks by different intiators at the same time. Sanjeev
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