EDIT: SOLUTION:

Nevermind, I am an idiot. As @ClickyMcTicker pointed out, it's the client side that is causing the trouble. His comment gave me thought so I checked my testing procedure again. Turns out that, completely by accident, everytime I copied files to the LVM-based NAS, I used the SSD on my PC as the source. In contrast, everytime I copied to the ZFS-based NAS, I used my hard drive as the source. I did that about 10 times. Everything is fine now. Maybe this can help some other dumbass like me in the futere. Thanks everyone!

Hello there.

I'm trying to setup a NAS on Proxmox. For storage, I'm using a single Samsung Evo 870 with 2TB (backups will be done anyway, no need for RAID). In order to do this, I setup a Debian 12 container, installed Cockpit and the tools needed to share via SMB. I set everything up and transfered some files: about 150mb/s with huge fluctuations. Not great, not terrible. Iperf reaches around 2.25Gbit/s, so something is off. Let's do some testing. I started with the filesystem. This whole setup is for testing anyway.

1. Storage via creating a directory with EXT4, then adding a mount point to the container. This is what gave me those speeds mentioned above. Okay, not good. --> 150mb/s, speed fluctuates
2. a Let's do ZFS, which I want to use anyway. I created a ZFS pool with ashift=12, atime=off, compression=lz4, xattr=sa and 1MB record size. I did "some" research and this is what I came up with, please correct me. Mount to container, and go. --> 170mb/s, stable speed
3. b Tried OpenMediaVault and used EXT4 with ZFS as base for the VM-Drive. --> around 200mb/s
4. LVM-Thin using Proxmox GUI, then mount to container. --> 270mb/s, which is pretty much what I'm reaching with Iperf.

So where is my mistake when using ZFS? Disable compression? A different record size? Any help would be appreciated.