> Since (M.2) NVMe to USB adapters exist, protocol conversion is certainly possible, and since such adapters are surprisingly inexpensive, presumably there's enough demand to drive down the price of the underlying controller chipsets.

> (These chipsets are, for example, the Realtek RTL9210B-CG or the ASMedia ASM3242.)

The NVMe to USB adapters aren't converting the NVMe protocol to another disk access protocol. They are USB3-connected PCIe endpoints, which allow the PCIe NVMe drive to connect to the host as an NVMe device.

This isn't equivalent to the protocol conversion the author is seeking, which would accept SATA commands on one end and translate them to NVMe on the other end. I would actually call that SATA drive emulation, not protocol conversion, as SATA and NVMe aren't 1:1 such that you can convert SATA commands into NVMe commands and vice versa.

They are USB3-connected PCIe endpoints, which allow the PCIe NVMe drive to connect to the host as an NVMe device

No?

https://us1.discourse-cdn.com/flex001/uploads/framework3/ori...

This is an RTL9210B NVMe enclosure. It's a UAS device (and I believe it supports BOT too.)

I have not examined this in much detail but I believe these converter ICs are actually rather powerful SoCs with PCIe host, SATA host, and USB device peripherals. The existence of firmware (several hundred KB!) for them is further evidence of this fact.

I don't believe this is true. Something like thunderbolt could allow this but the cheap commonly available ones "simply" appear as a USB disk and can't use any of the NVMe specific features like HMB, can't be secure erased with nvme-cli, etc. Lack of HMB support is a particularly painful limitation these days as dram isn't available on most new drives.