Why is my Raspberry Pi 4 too slow as a server?

> I bought a Kingston SNV3S/1000G NVMe drive. It supposedly can read and write at 6 GB/s and 5 GB/s respectively

That's a cheapo QLC drive making those numbers very conditional on several factors. Under sustained load it's not a surprise to see such drives drop to SATA speeds.

> So the limiting factor is the enclosure, that should still give me a generous 1000 MB/s.

That's capped by the USB controller, which means 512MB/s max.

I believe the USB controller still shares a bus with the NIC, which means maxing out the network connection will affect disk rw performance. You could confirm this by observing a concurrent iperf affecting fio results.

> The Raspberry Pi is notorious for not being excellent with encryption algorithms.

Well, that's specifically AES precompiles. Just like for kopia, you can benchmark and change LUKS algo for something more suitable for the platform like xchacha20: https://rr-developer.github.io/LUKS-on-Raspberry-Pi/

Author here, thanks for pointing out the mistake! The USB controller speed is indeed 4 Gbps and not 4 GB/s, I have updated the post accordingly.

> I believe the USB controller still shares a bus with the NIC, which means maxing out the network connection will affect disk rw performance. You could confirm this by observing a concurrent iperf affecting fio results.

Thanks for the pointers, I didn't know about iperf! That's something I'll likely try at some point for the sake of completeness, although I have other projects competing for my attention.

> Well, that's specifically AES precompiles. Just like for kopia, you can benchmark and change LUKS algo for something more suitable for the platform like xchacha20: https://rr-developer.github.io/LUKS-on-Raspberry-Pi/

Absolutely, that disk was encrypted using xchacha20. I used the excellent sdm project (https://github.com/gitbls/sdm) to make my Raspi boot from an encrypted disk. They have great documentation pointing out that xchacha20 should be used on the Pi 4 and earlier (https://github.com/gitbls/sdm/blob/master/Docs/Disk-Encrypti...)