How many SAS addresses should an expander has?

Seto, Pak-lung pak-lung.seto at intel.com
Wed Oct 16 13:03:36 PDT 2002


* From the T10 Reflector (t10 at t10.org), posted by:
* "Seto, Pak-lung" <pak-lung.seto at intel.com>
*
> In addition, in current SAS spec. individual links are 
> performing link initializaiton/speed negotiation 
> independently.  And it is not guaranteed that all links 
> within a wide links group to be negotiatied to have the same 
> negotiated link rate.  It may have problem if this wide links 
> group happens to have the lowest negotiated link rate on the 
> pathway between a particually initiator/target pair.  I think 
> the standard should either require all links within a wide 
> links group to negotiated to have the same link rate (I 
> believe it is a little bit to restrictive), or if any phy of 
> a wide links group when it is reporting it's link rate during 
> discovery to a initiator, it shall report the lowest 
> negotiated link rate of the wide links group that the phy is 
> belonging to (since the expander can select any link within a 
> wide links group to make a connection), because the initiator 
> has no concept of multiple minimum link rates for a pathway 
> connecting to a particular target.

The expander never reports a link rate for the port; it reports
everything on a phy by phy basis.  If a wide link consists of 
physical links running at different rates, the initiator will know.

Assume there is a wide link with both 1.5 Gbps and 3.0 Gbps physical
links.  If an initiator sends an OPEN (3.0) that needs to use that
wide link, that connection can only use a 3.0 Gbps physical link 
of that wide link.  If the initiator sends an OPEN (1.5), the 
connection may use a 1.5 Gbps link or a 3.0 Gbps link (with rate
matching by the expanders).

[Seto] This will make the expander a little bit more complex to build

Pak
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