[driver-discuss] Port Multiplier Support (sata framework)

[James C. McPherson]

On Mon, 08 Jun 2009 14:08:28 -0400
Miles Nordin <carton at Ivy.NET> wrote:

...

> supposedly you can plug SATA disks into SAS port multipliers, and then
> plug SAS port multipliers into SAS controllers. 

Yes, that's correct. It's part of the SAS2 spec.

> I think I heard on a
> list that compared to SAS PMP, SAS expanders are differently-designed,
> better, and supported by the proprietary solaris mpt binary driver,
> but never tried.  SAS expanders are exotic.
> 
>   http://www.supermicro.com/products/chassis/4U/846/SC846E1-R900.cfm
>   http://www.valleyseek.com/product.action?itemID=83883


My reading of the SAS2 spec is that what you refer to as "SAS PMP"
is actually just SAS Expanders. They're not exotic beasts, either.
Well ... _I_ don't consider them to be exotic. Dunno about your
definition :-)

A number of companies make them, too:

http://www.pmc-sierra.com/sas-expanders-loopswitch-chips/#expanders
http://www.lsi.com/storage_home/products_home/standard_product_ics/sas_expander_ics/index.html
http://www.vitesse.com (you'll have to search for them)


We've got LSI SAS expanders in JBODs (Jxx00 series) and on the motherboard
for 2RU and 4RU servers which will show up when you run "fwflash -l"
on NV.

The SAS expanders that I've seen all present a SCSI Enclosure Services
device to the host which is then ses- or (preferably) sgen-attached. They
also present an SMP device (Serial Management Protocol). At the moment
the only integrated drivers which support smp(7d) are mpt and mr_sas.
You'll note that both smp and mr_sas are in the Open side of the tree. 


James C. McPherson
--
Senior Kernel Software Engineer, Solaris
Sun Microsystems
http://blogs.sun.com/jmcp	http://www.jmcp.homeunix.com/blog
Kernel Conference Australia - http://au.sun.com/sunnews/events/2009/kernel