You can use hdparm(8)'s --dco-setmax option to reduce the visible size of most SATA drives. This is not particularly useful for single drives — leaving unpartit

You can use hdparm(8)'s --dco-setmax option to reduce the visible size of most SATA drives. This is not particularly useful for single drives — leaving unpartitioned space works just as well, assuming an OS that never writes to it — but it does stop TRIM-ignorant RAID controllers from potentially kneecapping SSD GC by "initializing" intentionally unused space. Though I imagine most RAID controllers initialize with zeroes, and I hope SSD firmware doesn't reserve flash to store large extents of zeroed sectors, so this shouldn't be terribly useful for underprovisioning purposes. But without extensive testing or access to SSD firmware algorithms, it's hard to say.