How to diagnose linux?

Question

linux

Nuclear button accordion theme, excuse me)
Guys, I have Nas QNAP 219-II.
The disk in the array died, changed it to new ones, reinitialized it for reliability, rolled up the latest firmware and now I'm testing the Kama Sutra.
Either the shared folders are no longer visible, or it hangs so that after authorization through SSH, the terminal does not issue anything further, you have to hard reboot.
The logs show nothing, only "Raid file system" error after a hard reboot, then the file system test passes without errors.
There is no overheating, the inside of the iron is clean.
I'm blonde in Linux, I only know simple commands...
Is there a way to find out where "titanic" begins? -for example, which process stops responding ... to understand if it's time for iron to retire or it doesn't drag something ...

Answer 1

What logs did you look at? Is there something similar to Ubuntu?