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What is the need of Wide port in a SAS Controller?

Posted on 2011-02-28
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In a SAS Controller, as opposed to a narrow port, Wide port has 4 phys per port. All the 4 phys share a common SAS Address. My question is where is this concept of "Wide port" used in real world? and how exactly it achieves the advantages that it claims to provide?
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Question by:raj_ksrt
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by:dlethe
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No, all 4 ports do not share the same common address.  They share the same expander, but every disk has a unique WWN.   You are simply looking at a connector that you can plug a single cable into that "expands" into 4 SAS cables.  
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andyalder earned 500 total points
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SAS wide ports (either 2, 4 or 8 PHYs combined) aren't used for disk to controller but they are preferable for expander to expander and controller to expander (e.g. hanging an external 25 disk enclosure of a RAID controller's external port) to give bandwidth agrigation.

http://www.scsita.org/aboutscsi/sas/tutorials/SAS_Arch_Overview_public.pdf is a bit out of date but still a good bedtime read.

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by:andyalder
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For example in the wide world, HP Smart Array P800 with a MSA70 uses a 4 PHY wide port that has a single SAS address.
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by:andyalder
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Additional hidden example in the above, the Smart Array P800 has a LSI ROC IC linked to a PMC-Sierra expander IC which also uses a wide port to join the two chips together.

So to get to the disk in the cage the data goes over two wide ports (one between ROC and expander on the P800 and one between expander on P800 and expander on MSA backplane) and then over a single PHY port from the fanout expander on the backplane to the disk.
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by:andyalder
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Dlethe didn't address the subject of a wide port at all, he described a fanout cable which uses 4 narrow ports.
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by:Qlemo
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Yes, you are right. Why didn't you object?
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by:andyalder
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Hadn't thought of objecting, recommend 34999210 as answer.
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by:Qlemo
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I recommend http:#a34999185 instead - more info.

Qlemo
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by:andyalder
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Excellent choice, thanks Qlemo.
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by:WhackAMod
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Restarting closing process
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