The PINEBOOK Pro M.2/NGFF NVMe SSD Interface Adapter

[fire219]

Is there some kind of upper limit in terms of throughput for the NVMe on the SoC side of things? I assume if you get some fancy Intel Optane thing it'll start to hit some other system limits

The limit for throughput is the PCIe interface that the NVMe communications are going through. In this case, it is a PCIe v2.1 x4 link.

A single (x1) PCIe2 link has a theoretical bandwidth of 500MB/s. More lanes adds more bandwidth in increments of 500MB/s. Therefore, the x4 link can theoretically do 2000MB/s (or in simpler terms, 2GB/s).

Those are just theoretical numbers, however, and reality is imperfect. There's also control signals and whatever else that has to go over that link. Reality is likely going to be somewhere around 1.5-1.7GB/s.

And similarly for the mSD. Is there an upper limit to the class that is supported? (past which you won't see any perf benefit)

I believe that the limit for what the microSD slot can support is UHS-I. Its fastest mode is "SDR104", which provides theoretical speeds of up to 104MB/s.