The TL;DR version is:
- there’s no size limitation with NVMe SSDs
- since Rock 5B (RK3588’s PCIe30X4(4L) controller [1]) maxes out at Gen3 x4 if you buy an SSD capable of Gen4 speeds (or better) take care that it is not just x2 since this ends up with degraded speed: Gen3 x2. Buy a x4 SSD if you’re after maximum performance (though buy quality SSDs anyway since cheap SSD garbage will underperform always regardless of interface specs)
- if you don’t care about performance buy whatever fits as long as it’s not garbage (faking capacity or SMART values)
[1] RK3588 consists of 5 PCIe controllers to provide PCIe Gen3 with 4 lanes max and Gen2 with 3 lanes max, the latter pinmuxed with SATA/USB3:
