Michael Evans wrote:

seems to be only one manufacturer, and only one seller currently.  I
guess most people building >6 drive arrays have the cash to waste on
limited boxed solutions or higher-end hardware controllers that
abstract the details (and often flexibility) from the system.

Or use dumb LSI SAS controllers (sas3442e-r with IT firmware loaded, 
$200) and port expander based chassis that allow considerable 
flexibility regarding md RAID and number of SAS/SATA drives attached.

The only current caveat that is being worked on, is that use of 
smartmontools causes drives to disconnect.

Regards,

Richard