Updates to Files On-Demand on macOS

Rick_Baumhauer  It's not slower performance that I worry about - it's actually running out of space sooner or later. My space needs gradually expand, which I think isn't uncommon. When I first bought my previous MacBook Pro in 2018, for a long time the internal drive was only 20% full. Then in 2019 I discovered Sibelius and started to compose with it, generating large MIDI files which quickly started taking up lots of space. I could see the handwriting on the wall there, so I bought a 4 TB external WD Passport HD and partitioned it into 2 equal volumes,, one for data and one for a Time Machine Backup (yes, for a long time I was dumb enough not to back up my data). I also edit those MIDI files with Audacity. But as you say, an HD is slow, and it often takes a minute and more for Audacity to write an edited MP3 to disk. And ultimately my Time Machine volume started filling up, and now it takes Time Machine over 2 hours to do each "hourly" backup because it needs to frequently stop to free up space. So I'd like to repartition the Passport to use all 4 TB for backup. If I had to put my data that's now on the 2 TB volume on the 512 GB internal drive, it really would be very full.

All that to reiterate that I knew I would need more space, sooner or later, the problem was that I had no idea that I'd be up against a total roadblock trying to make an external SSD work. Eventually I really will need 2 TB of fast disk space, and there is no way a 2 TB internal from Apple would fit my budget.