How to backup data from one external drive to another (one-way)

Solution 1:

I've just bought another 5TB external disk (Seagate backup plus portable), where I always would like to have a 1-1 copy of the whole date from the first disk.

It’s not a sound strategy to back up a backup.

I write about this in much more detail in another related answer, but to summarize here, you should have distinct backup jobs, not copies of existing backups.

Having an “identical copy” of a drive is good for redundancy and the correct tool for that job would be a product that implements RAID where the drives are mirrored. Manually (meaning non-RAID) syncing drives falls short of being a good backup solution because if there are issues with the original backup (i.e. file corruption), the same issue is replicated to the other drive making the backup useless.

Syncing is a tool best used when you need to have files accessible in/from different locations and are typically not being simultaneously accessed (changed).

What you should do with your current setup is continue to use the MyBook for your daily backup and then create a new backup job that does a differential (only what has changed) backup when you plug in the Seagate.

Solution 2:

You could do it yourself with rsync but if you want a better, more Mac-like / GUI experience, I’d recommend Carbon Copy Cloner.

It will only copy over the files which have changed, and it can be set to sync whenever a disk appears, or it can manage mounting and unmounting the second drive on a schedule. I’d have it set to run at like 1:00 a.m. so as to not use system resources while I am using the computer.

I also own ChronoSync and SuperDuper, but I think CCC is the best / easiest tool for the job. I’m pretty sure there’s a free trial period, so you can test it out and see how it does.

Solution 3:

You are looking for a file syncing app. There are many to choose from.

Chronosync and SuperDuper, are apps that I have used for different purposes, but there are many others.

PS: Answer me this: if you accidentally delete a file on your 1st external, and then the 2nd drive synchronizes and deletes the file: how will you recover that file?