fio VS xNVMe

Assuming two systems use flash storage, network bandwidth is identical and it is configured the same way, there should be an issue within the PC, either system or storage drive. Check the system logs for errors and warning events related to data transfer from/to NAS. Try to benchmark the PCs' disks using fio to confirm they have similar performance. https://github.com/axboe/fio

Not specifically addressing your question, but when you get to the point of wanting to start doing some experiments you may find that 'fio' [1] is very handy.

[1] https://github.com/axboe/fio

The dd is not a good benchmarking tool, you should use something like fio and probably tune it to use the ioengine most similar to your use case (eg. a database server will probably use some async IO interface). In your first example (with bs=1G) probably something (the guest OS, the qemu/kvm or the host OS) have split into smaller chunks anyway.

All linux tests are run with fio 3.32 (github) with future commit 03900b0bf8af625bb43b10f0627b3c5947c3ff79 manually applied.

FIO: https://github.com/axboe/fio

Agree, I used flex/yacc to add an arithmetic expression evaluator to fio a few years back to allow simple math with some units in fio's job files, and for stuff like that, they're fine, but I wouldn't want to use them for a real language, the error handling is kind of a nightmare.

Flexible I/O Tester (fio-3.33): https://github.com/axboe/fio

Basically io_uring grew a lot, the latest API offers incredible tools but there are very few examples in any language (xnvme and fio), and in particular I'm struggling to understand how to do it in Rust: where should unsafe code stop? should I simply expose the io_uring api as unsafe, or should I do more work in C and present the ring when ready to rust?

The foundation of xNVMe is libxnvme, a user space library for working with NVMe devices. It provides a C API for memory management, that is, for allocating physical / DMA transferable memory when needed. An NVMe command interface allowing you to submit and complete NVMe commands in a synchronous as well as an asynchronous manner. Similar to libnvme, however, with a focus on I/O performance and portability. Thus, xNVMe and the libxnvme library works not just on Linux, but also on FreeBSD, Windows, and MacOS.