Hi,
I am setting up a backup server to provide back for my Samba based NAS.
My question is whether i should use another samba server or an ftp server is better for computing resources requirement. In other words, which one, the samba or the ftp server is lighter.
thanks
If you cannot use NFS for some reason, FTP is lighter.
So instead of SMB, NFS is lighter and better for hosting backup files?
It is lighter. Regarding what is better for backup files, it has to do with the local file system.
on NFS you could preserve file system permission and owner, while on SAMBA this might be lost if you copy files over
rsync would probably be a good idea…
https://www.2daygeek.com/linux-rsync-scp-command-in-reverse-mode/
https://medium.com/axcess-io/understanding-rsync-and-scp-46bcb20791d0
This way you could rsync thru scp and only upload the changes and not eat up all your valuable bandwidth
well rsync is a tool t copy data but you still need the server hosting the target directories. And for this NFS would be best option. And yes, if this is setup, you can use rsync to backup the data 
My last question on the topic is cifs. I just want to understand it correctly.
So samba and cifs used to be different sharing protocol, but now it is united and by installing samba, cifs is also installed along, and makes multi user environment possible. Am i correct?
Well CIFS is a form of SMB. There no real difference if it comes down to file system permissions.
I see. The question emerged while setting up a multi user smb environment. When i installed smb, cifs was also installed.
maybe we misunderstood each other. I was talking about to keep file system permissions while saving data from DietPi to an NFS share. But I guess you like to setup a file server on DietPi to be able to backup data from extern to the DietPi device.
Of course you can setup a multi user environment using SAMBA. As well you could control the directories each user can access.
About the terminology of SMB/CIFS/Samba:
SMB is an open defined transport protocol.
CIFS is the common particular SMB implementation on current Linux distributions. Theoretically there could be others, but practically both terms mean exactly the same.
“Samba” is the common particular SMB/CIFS server implementation used on current distros.