How many SAS addresses should an expander has?

Seto, Pak-lung pak-lung.seto at intel.com
Wed Oct 16 07:37:00 PDT 2002


* From the T10 Reflector (t10 at t10.org), posted by:
* "Seto, Pak-lung" <pak-lung.seto at intel.com>
*
First, ignoring the STP/SATA attachment first.

For all links within an expander, during the Identify address frame phase,
according to the SAS address field definition on page 127 v2.0a

"An SAS ADDRESS field indicates the SAS address of the device transmitting
the IDENTIFY address frame."

>From the above definition, it means if any number of links from an expander
are connected to an end devices, it will automatically (wants to) become a
group of wide links and there is no choice of keeping it as individual
separate links?  Also, what happen if the SAS Addresses received from the
end device(s) are not the same for all those links?

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.

Pak
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