I just spawned a r6a.16xlarge with a 25gbps NIC, created a 10GB file which I uploaded to an S3 bucket in the same region, through a local S3 VPC endpoint.

Downloading that 10GB file to /dev/shm with s5cmd took 24s, all while spawning 20 or so threads which were all idling for IO.

The same test using a Python tool (http://github.com/NewbiZ/s3pd) with the same amount of workers took 10s.

Cranking up the worker count of the latter library until there is no more speedup, I can reach 6s with 80 workers. That is, 10/6 = 1.6GB/s, which seems to confirm my previous comment.

What am I doing wrong ?