I have a secondary disk on my arch install, but by default is not really mounted, this is the storage disk where I keep my download, musics, and videos, so I wish I could have it mounted by default at startup, is there a way I could do this either from KDE or natively from linux?

Thanks for your question, I have the same problem. I'll wait for any answer.

Seems this cant be done in KDE or shouldnt, but is a linux question, by editing the /etc/fstab file and adding the disk to it. I recommend using blkid or list the /