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

Posted on 2011-02-28
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Last Modified: 2012-05-11
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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12 Comments
 
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Expert Comment

by:David
ID: 34998011
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 2000 total points
ID: 34999185
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http://www.scsita.org/aboutscsi/sas/tutorials/SAS_Arch_Overview_public.pdf is a bit out of date but still a good bedtime read.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
ID: 34999210
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
ID: 34999859
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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Expert Comment

by:andyalder
ID: 35412130
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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Expert Comment

by:Qlemo
ID: 35412358
Yes, you are right. Why didn't you object?
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by:andyalder
ID: 35412481
Hadn't thought of objecting, recommend 34999210 as answer.
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by:Qlemo
ID: 35412489
I recommend http:#a34999185 instead - more info.

Qlemo
Cleanup Volunteer
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by:andyalder
ID: 35412517
Excellent choice, thanks Qlemo.
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by:WhackAMod
ID: 35446419
Restarting closing process
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