From: "Craig Stoops" <craig@expertio.com> To: "'Sheffield, Robert L'" <robert.l.sheffield@intel.com>, "'Day, Brian'" <Brian.Day@lsi.com>, <t10@t10.org> Subject: RE: SAS 2 Muxing and DISCOVER Date: Tue, 15 May 2007 08:52:13 -0700 X-Message-Number: 7781 Formatted message: HTML-formatted message Hi Bob Sheffield (and others), My purpose isn't to change the standard, but to clarify it. I can find nothing in the standard to prevent each logical phy from having it's own address, and in fact in section 4.1.2 (of 9a), the words are pretty supportive of this possibility where the spec describes that a physical phy may operate as 2 complete logical phys and lists the characteristics. There is nothing in any of the other sections to say one way or another. I also don't see a way to enforce that the same address be used on the two logical phys, and other than Discovery, it works fine - the two logical phys either look like a wide port, or two single phys. I do have to differ with section 4.1.2 a bit, in that phys don't really have addresses. The way the standard is written, addresses and IAFs belong to the link layer (SLIR) and MA and not the phy layer, but that's another matter for discussion. I'll state a fairly obvious example of a natural use for muxing. Since the point of muxing is to effective use a 6Gb link to communicate with two 3Gb devices, using muxing is is possible to build a very cheap active-active mux with NO embedded processor and NO embedded expander function. Using muxing, this part has one 6gb host port, and two 3Gb (or 1.5 Gb) ports to connec the devices to. If each logical phy connected to the host has it's own SAS address, there is no internal arbitration for links, and no processor required to make this work. Now someone might say, "but link multiplexing can't be required", however an OEM can require anything they want in their box. And active-active muxes appear to be a very hot commodity right now given the number of companies that have them in development, and this demand is being driven directly by OEM requirements. Please do not construe my comments one way or another as supportive of Multiplexing in general. But if we are going to have it, we should deal with the issues. Craig Stoops ExpertIO, Inc. "Your Storage Verification Experts" www.expertio.com 805-428-0839 -----Original Message----- From: Sheffield, Robert L [mailto:robert.l.sheffield@intel.com] Sent: Monday, May 07, 2007 4:25 PM To: Day, Brian; craig@expertio.com; t10@t10.org Subject: == SPAM == RE: SAS 2 Muxing and DISCOVER Craig and Brian, Saw my name mentioned in this thread. I think what's being suggested is that it might be a reasonable thing for logical phys to be in different SAS ports, even if they share the same physical phy. This would require changing the standard, andI haven't heard a good argument to say why it wouldn't work. Nobody has posted a proposal showing the changes that would allow this. Bob Sheffield Intel Corporation _____ From: owner-t10@t10.org [mailto:owner-t10@t10.org] On Behalf Of Day, Brian Sent: Monday, May 07, 2007 3:28 PM To: craig@expertio.com; t10@t10.org Subject: RE: SAS 2 Muxing and DISCOVER Craig... Actually, the current 9a draft of the spec (it was also present in revision 9) does require all logical phys/links for a physical phy/link have the same SAS address. The statement is in section 7.8.2, saying: "The IDENTIFY address frame sent by each logical phy in a physical phy shall be identical." Based on that requirement, logical links within a muxxed physical phy would then always be in the same wide port. And provides a reason that keeping the discovery based on physical phys is sufficient. Brian Day LSI Corp. _____ From: Craig Stoops [mailto:craig@expertio.com] Sent: Sunday, May 06, 2007 10:09 AM To: t10@t10.org Cc: Day, Brian; 'Sheffield, Robert L' Subject: FW: SAS 2 Muxing and DISCOVER Rob (Elliot), I don't think anyone responded to this. I have seen several proposals (one from Robert Sheffield) that discuss handling of virtual phys (in an expander) but none talking about logical phys that have been created by the addition of muxing. Logical phys for a physical link need not have the same address, and may or may not be part of the a wide port. Does anyone have a proposal on how this (discover and reporting) should be handled? Thanks, Craig -----Original Message----- From: Craig Stoops [mailto:craig@expertio.com] Sent: Wednesday, March 14, 2007 8:11 PM To: 't10@t10.org' Subject: SAS 2 Muxing and DISCOVER Rob, Steve, Brian and others involved: I'm wondering about SMP Discover and interaction with Muxing. I've read the recent proposal 07-091r0 regarding the Discover extensions, but I feel there are some issues at hand. >From a higher perspective, there isn't much difference between 2 logical phys with muxing and 2 physical phys. Each logical phy sends and receives an Identify Frame (IAF). As such, each logical phy is free to advertise any capabilities it sees fit, including a unique SAS address. The two logical phys need not send the same information. The net result is, that the 2 related logical phys may either be viewed as 2 logical ports, or two phys as part of a wide port. I know that when Muxing was suggested that being seen as a wide port is what was in mind, but I can think of several target devices that would like to advertize two different SAS addresses on the muxed link. There is nothing I can find in the standard to prevent this, and modeling show it works very nicely. To the higher level layers such as port layer of Expander Function, there is no difference between a muxed link and a non-muxed link. Only the SAS addresses on that link determine whether the logical phy is part of a wide port or not. However, this implies that when addressing a SAS device that has muxing enabled, that it should report the number of phy as as the number of logical phys, not physical. And also, it needs to be possible to issue a Discover to each logical phy, not just physical phy inorder to gain access to the individual IAF results. Another potential solution is to issue Discover for Phyical phys, but have space to report the capabilities of each logical phy that is part of that phycial phy, eg two attached sas address, two sets of capbiltiies (both local and remote), etc Comments? Craig Stoops ExpertIO, Inc. "Your Storage Verification and Design Experts" 805-428-0839