Expander device type discrepancy

Hugh Curley hcurley at indra.com
Mon Jul 22 06:15:51 PDT 2013


Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r1307221_f.htm">HTML-formatted message</a>

Hello Apoorva,
SAS 1.x defined two types of expanders: Fanout Expanders which knew of 
all the devices in the SAS domain, and Edge Expanders which knew of the 
devices attached to it. Edge expanders could do subtractive routing ("I 
don't understand this address, you handle it") for addresses they could 
not resolve; fanout expanders could not do subtractive routing (if they 
did not recognize the address, it did not exist in the domain).
Expander manufacturers did not make a true fanout expander, nor a true 
edge expander, but one model that could function as either. SAS 2 simply 
recognized what was happening in the industry and also removed the 
distinction between fanout and edge expanders.
So in the Identify address frame, 011b states "Expander device compliant 
with SAS 1.1", which is obsolete.
Perhaps they should both state the same thing, but there is actually no 
discrepancy.
Thank you,
Hugh Curley
KnowledgeTek
On 7/22/2013 4:40 AM, Apoorva Vats wrote:
>
> Hi,
>
> As specified in  "SAS Protocol Layer - 3 (SPL-3) " version 
> specification (T10/BSR INCITS 492)(Revision 02 / 16 January 2013)
>
> In case of "IDENTIFY ADDRESS" frame
>
> Page no. 328
>
> The DEVICE TYPE field indicates the type of device containing the phy, 
> and is defined in table 119.
>
> Table 119 --- DEVICE TYPE field
>
> *Code*
>
>	
>
> *Description*
>
> 001b
>
>	
>
> End device
>
> 010b
>
>	
>
> Expander device
>
> 011b
>
>	
>
> Expander device compliant with SAS-1.1
>
> All others
>
>	
>
> Reserved
>
> Here "DEVICE TYPE" field in IDENTIFY ADDRESS FRAME specifies 2 types 
> of Expanders
>
> But in case of "SMP DISCOVER" response:
>
> Page no.*652*
>
> The ATTACHED DEVICE TYPE field indicates the device type attached to 
> this phy and is defined in table 269.
>
> **
>
> *				  Table 269 --- *ATTACHED DEVICE TYPE 
> *field*
>
> Code
>
>	
>
> *Description*
>
> 000b
>
>	
>
> No device attached
>
> 001b
>
>	
>
> SAS device or SATA device
>
> 010b
>
>	
>
> Expander device
>
> 011b
>
>	
>
> Obsolete
>
> All others
>
>	
>
> Reserved
>
> Here "ATTACHED DEVICE TYPE" only specifies single type of Expander.
>
> In "IDENTIFY ADDRESS" there are 2 types of Expanders specified but in 
> case of "SMP DISCOVER "response frame only single type of Expander is 
> specified.
>
> Please help me understand about this discrepancy.
>
> Regards,
>
> Apoorva
>



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