For authoritative and focused answers, I'd like to place an exceptionally large bounty on the following question. Before I do so – no rush – is the question understandable?

(Is it clear enough that the question is not about TRIM Enabler and the like? And so on.)

Also, mystery surrounds the reason(s) for some types of flash/solid state drive showing activity (typically a flashing LED) after unmount of all volumes. I'm tempted to add that as background to the question – conjecture that in some cases, the post-unmount drive activities involves TRIM – but that conjecture could devalue the thing that's to be bountied. Thoughts? Thanks.

@GrahamPerrin I think you did a great job explaining you want to know how the core OS works with third party drives.

Whether people obey that part due to the length is another story, but a nice comment can help there and even wrong answers help others from time to time :-)

@bmike Thanks. The question is now just a little longer (!) but the reorder, and the two quotes, might make it easier to digest when I add a bounty in … maybe two days' time.

Excellent findings.

200 bounty or 500? Gut feeling?

I wonder how TRIM works on USB and thunderbolt connected drives - but have been too busy to poke around. I'm guessing your drive is internal to the Mac on the SATA bus?

sshd internal to a MacBookPro5,2. The question is less for me – I'm happy with things – more for the benefit of other people.

That said, I have personally seen the flashing-after-unmount effect (conversation above) on, maybe, a handful of simple USB flash drives.