Thank you for taking the time to explain that!
I think I have been needlessly over-complicating this, and I somehow confused myself into thinking that drive wear leveling was at least partially dependent on TRIM.
Admittedly, I haven’t exactly been enthused about using TRIM as it was blacklisted for certain Samsung drives for years in the Linux kernel, but that was a very long time ago.
TRIM absolutely helps wear leveling, because it allows the drive to know about every sector on the drive that’s available for write. Without it, the drive can’t know if any given cell that has stored a write is still necessary, because it doesn’t know when the filesystem marks the data stored in those cells as deleted.
So, without TRIM, the drive essentially has to wait for the filesystem to ask to write to the same virtual sectors, before it knows that those virtual sectors are available for new writes. Since the filesystem has no knowledge of or visibility into the raw physical media of the drive, the filesystem can’t and won’t manage that layer as well as the drive’s firmware could.
There just still isn’t any effective difference between reserving space by partition, by quota, or by “saving less stuff.” None entirely resolves the problem–particularly in the long run–and none of them does so more effectively than the others, in terms of the actual ordering of data on disk.
That leaves the human element to consider–and if partitions make more sense to you intuitively than a ZFS quota, use them! Or if partitions and quotas alike seem like more of a pain than a relief when you could just save less stuff… Just save less stuff! Or if you want a hard boundary imposed right now, but want to be able to lift that boundary very quickly and easily if necessary… There’s the case where a ZFS quota is your best tactic.
Again, thank you for putting me on the right path!
Admittedly, my configuration without TRIM is less than ideal, but with a little TLC it works reasonably well.
Next time I know HBA TRIM support will be at the top of my shopping list. 