I never really know if I’m reading/writing to/from the SSD or the platters. I mean, it seems zippy so my inclination is just to leave it as-is and trust that Apple knows what they are doing.
I have entertained the idea of splitting up the fusion drive and trying to manage the SSD space on my own but thanks to this post, I’m feeling less inclined to do so. Rauol Pop did it and then ran some tests that show splitting the drive up yields equivocal benefits and some measurable negatives so, I’m trusting that the engineers at Apple know what they’re doing.
That, and I’m making good use of 24GB of RAM and just loading up all my applications into RAM anyway, so, there’s that. Also, as soon as they come down in price just a smidge, I’m going to pickup an external SSD that supports Thunderbolt 3 like the Samsung X5, that ought to be pretty close to the speeds of the internal SSD.