A friend in Bali handed me a 1 terabyte external SATA drive recently and that’s great because the device is an integral part of a 3-2-1 backup strategy I’m adopting after Apple Care suggested I make a full backup of my 15" MacBook Pro.

The principle is simple:

3 copies, 2 different types of storage (physical and in the cloud for example) and one copy being physically separated from the others

Emanuele M. Monterosso

Of the 3 copies I needed 2 are complete. One copy is stored on MicroSD and kept with me. The other encrypted in the cloud on a Scaleway server in France. The last copy is going on the external SATA drive given to me last week which would be cool to put in a time capsule.

In this post I will show you how to securely store your backup data with two layers of encryption on an external drive or disk. After securing the disk we will start to automate the creation of space-efficient backups. Tools we’ll be using include GNU Parted, DMCrypt, a device-mapper crypto target, and Borgmatic to automate our backups in a expressive way.