Clone and then copy to a second external drive ??

[brantwinter]

Hi - I have been a happy SD using for a few years now, but I think I must be getting more and more paranoid !

I currently run a full bootable backup to an external USB drive and would like to then copy this to my NAS disk.
I have tried rsync ( manually ) after a SD copy has completed and I am met by all sorst of errors as rsync tries to copy the files across. I have tried runnign my rsync script with sudo but no luck. The errors are strange I/O type errors after rsync has copied about 50Gb of the data.

Does anyone else make a second full copy of theor SD backup after completion, if so how ?

Thanks in advance.