I'm running a spin-off and the team is still small. So, I was wondering how a minimal backup system should be. I do not mean to use github, that we already use, I am concerned about the HD of our servers and laptops. Thanks in advance!

Best to make a recovery plan not a backup plan. Think about different scenarios and how you deal with it. If a laptop disk dies yes you may loose data but hopefully the dev pushes their branch often. How long will it take that dev to get running again and what is the cost of them not having a computer? maybe you could keep a spare laptop on hand.

Is their customer data on your server? how bad would it make your company look if you lost their data? If you back it up is the backup safe? how long would it take you to recover?

Some of the more advanced nas units has backup software with support for keeping a few versions on a rotation

For even more lightweight just set up an old workstation with some extra disk and a scheduled script to copy over data.

I prefer to have at least more than one copy from more than one day so a corrupt file copy cannot destroy all copies

By dumping output from the copy to s file and using grep or similar simple file parser you can have it mail you in case of copy error.

Thank you for your advises. I have been defining the recovery plan and maybe I need some kind of RAID controller for the data distribution across multiple HHDD. Moreover, It should be ideal to use NAS units with RAID.