AFAICT, a SAS expander should also support SATA drives. Can anyone
> confirm that -- or, is it an "implementation defined" condition?
> (I have external enclosures thusly enabled)
I'm 80% certain that you can put a SATA drive on a SAS controller via a SAS expander without any problems.
And, can anyone recommend an *internal* SAS extender (I don't want/need
> an external enclosure as all of the drives are 2.5" SSDs and, thus,
> considerably smaller than 3.5" magnetic disk slots) that would handle
> a dozen or more?
I've seen multiple half height and full height 5-1/4 bay modules that will accept multiple 2-1/2 inch drives. The half height versions could hold six drives horizontally and the full height versions could hold many more vertically.
Check out the usual electronic haunts; Amazon, ebay, etc. I like Amazon in that as a Prime member, it's quite easy to return something (in good condition) if it doesn't work.