Best backup solution for about 1tb of data?

Heya, I wanted to ask what the best backup solution would be for a RAID 1 array, with approximately a terabyte of data on the NAS (that is slowly growing by the day). I have an external 4TB HDD connected, and would like to know what the best method of copying this data over is. I've heard that just using rsync or a tar command every hour on a cron job is fine, but with my recent attempt, it takes me at least 30 minutes to copy a 90gb file stored on the NAS while using rsync.

I am using a raspberry pi 4 as my NAS device.

Any help is greatly appreciated, thanks in advance.

Quote from BlueCoffee

1 on 1 backup is what I use with rsync.

If the files are small and lots it will take ages. I have all my rsyncs run at 1am.

what do you mean by "1 on 1"? as in a complete uncompressed clone of the data? and if so, what way could i set this up. im presuming a cron job running an rsync command every 1am. but what if it needs to use sudo? as i believe i will have to as part of my setup.