Excessive and weird server lag on a huge modpack

[Demokdawa]

Hi !

I have a server with the pack "Meatballcraft" installed, and while the client is butterly smooth compared to everything i played in my life of modded MC, the server is experiencing insane levels of lags. And no, it's not because the cpu it's a 4c/8t 4,2 ghz is not enough or not enough args, or java args or wathever. 

Even if the final answer would be something like "it's because mods are bad and too much for the server", i want to try to understand whats the problem here and what is happening.

Why do i post here ? Because i profiled the server with spark, and i don't understand from where the lag comes from (i have NOTHING running, no farms, no quarries, no mod that would do chunk updates, nothing).

Here is the result of the profiler running for 10 mins with NO PLAYERS on the server.

https://spark.lucko.me/p4wu4zRVUC

On the spark profile, you can see that 85% of the tick thread is used to save chunks (there was no backup processes while the profiler was running), and it suppose interact with chunk data and player data.

I know machines on modded servers can cause huge ticks rates/blocks updates/entities updates and lag the server, and it's the same for generation of new chunks.

But here we talk about the game just having a hard time reading chunk files and saving them on a server with no chunkload and no players.

If anyone have an idea, please share, it drives me mad.

Ty in advance !