How to utilize a PCIE4.0 SSD?

[Stefan Lederer <lederers@hs-furtwangen.de>]

Hello dear list,

(I hope I do not annoy you as a simple application programmer)

for a seminar paper at my university we reproduced the 2009 paper
"Pathologies of big data" by Jacobs, where he basically reads a
100GB file sequentially from a HDD with some light processing.

We have a PCIE4.0 SSD with up to 7GB/s reading (Samsung 980) but
nothing we programmed so far comes even close to that speed (regular
read(), mmap() with optional threads, io_uring, multi-process) so we
wonder if it is possible at all?

According to iostat mmap is the fastest with 4GB/s and a queue depth
of ~3. All other approaches do not go beyond 2.5GB/s.

Also we get some strange effects like sequential read() with 16KB
buffers being faster than one with 16MB and io_uring being alot
slower than mmap (all tested on Manjaro with kernel 5.8/5.10 and ext4).

So, now we are quite lost and would appreciate a hint into the right
direction :)

What is neccesary to simply read 100GB of data at 7GB/s?

I wish everybody a happy new year!
Stefan Lederer