Re: SAS v SATA interface performance

[Richard Scobie <r.scobie@clear.net.nz>]

Greg Freemyer wrote:

> Also, if you have Port Multiplexers (PMPs) in use, that would be
> interesting to know.  I don't even know if PMPs are supported via SAS
> controllers in 2.6.24 or not.  ie. PMP support is new to 2.6.24 and
> only a few Sata controllers will have PMP support in 2.6.24.

No, port multipliers are not in use here, the technology that SAS uses 
is called port expansion. While I do not know much about the low level 
operational differences, from a performance perspective, this is my 
understanding.

Port multiplication only permits one drive to be accessed at once, 
whereas port expansion allows multiple drives to be accessed simultaneously.

Port expanders are selfcontained and do not require kernel support - the 
only kernel requirement, is support for the SAS HBA or RAID controller.

See Xtore, Adaptec or Dell (MD1000), for suitable JBOD enclosures.

Regards,

Richard