On Tue, 2005-05-24 at 20:25 -0400, open_iscsi wrote: > The MC/S feature of iSCSI is not multi-pathing. Multi-pathing would be the > use of multiple sessions to reach the same target. Generally the two > sessions would use the same InitiatorName+ISID but use different Target > Portal Groups at the target. In SCSI terms, it is the same initiator > accessing different SCSI ports. Well, yes, every driver vendor with a multi-path solution in-driver that made a single presentation to the mid-layer has argued that one... The bottom line is that implementation must be in-driver. So every driver doing it this way has to have their own separate multi-path implementation. Whether you call it FC/AL or MC/S (or any of the other buzz acronyms) it's still a driver implementation of pathing. > MC/S can be used to improve band width of a session without using > multi-pathing and it belongs in the driver because it is hidden from the > upper layers. Think of it like parallel wires, each carrying separate (but > sequenced) commands in parallel. So far, no-one has been able to produce any figures to show that MC/S is significantly better than symmetric active dm-multipath to an iSCSI target, but if you have them, please publish them. Hiding something from the upper layers which the upper layers could do equally well themselves is what's considered wrong: it adds code bloat with no tangible benefit. James - : send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
