How to make the most of a backup drive on the Apple Mac

A backup drive, such as a USB device, is an essential component of any computing system and you should make Time Machine and other backups with it. Here is one way to use it efficiently.

A backup drive is a USB drive that plugs into the Mac and it usually sits on the desk beside the computer attached by a cable. However, it could be wireless or a NAS (network attached storage) drive.

Old style hard disk drives (HDDs) are big and cheap and this makes them useful as backup devices. They are much slower than solid state drives (SSDs), as used in MacBooks these days, but this matters much less for an external backup system than it would for an internal drive. If you can afford a big SSD for a backup drive, then go for it, but an HDD is fine.

There are many ways to use a backup drive and there probably isn’t a best way. This is the way that I use mine and it is a bit unusual, so it might give you new ideas for ways in which you can use your own backup drive.

Mac and backup drive

Drives come in a wide range of capacities and yours may be different to mine. It does not matter. You may need a bigger backup drive if your Mac’s internal drive is bigger than mine or you may be able to allocate more space to various backups if your USB drive is bigger. Adjust things accordingly.

  • I have a MacBook Air with a 256 GB drive
  • I have an old USB drive with a 500 GB disk
  • The MacBook’s has a 154 GB partition with macOS
  • The MacBook’s has a 96 GB Windows Boot Camp partition

I want to back up macOS in two ways, a SuperDuper! backup, which is a bootable external drive with an exact copy of the Mac’s internal drive, and a standard Time Machine backup. If there is a disk disaster, I can boot from the backup drive and carry on working and there is almost no downtime.

I therefore need three partitions on the backup drive. Here’s how they were set up.

Partition the USB backup drive

The backup drive is an old one that has been used many times for various purposes. USB drives are usually supplied FAT formatted because they can then be accessed by an Apple Mac or Windows PC, so if necessary, start Disk Utility, select the drive and click Erase. Choose Mac OS Extended (Journaled) for the filing system.

Disk Utility in macOS on the Apple Mac
Erase a USB drive and select Mac OS Extended (Journaled)

This is my 500 GB USB drive ready for partitioning. Select the drive on the left and click the Partition button in the toolbar at the top.

Partition a drive with Disk Utility on the Apple Mac
Partition a drive with Disk Utility

The first partition will be used for SuperDuper! backups, which is basically a clone of the Mac’s internal drive. The macOS partition is 154 GB, so I set the partition size to 150 GB. It does not have to be the same exact size, just big enough to store all the files. I set the name to USB SD (SuperDuper!).

That leaves 350 GB of unused space on the 500 GB drive. After selecting the unused space, the Partition button is again clicked and this partition size is set to 270 GB. It will be used for Time Machine backups, so it is named USB TM.

Partition a drive with Disk Utility on the Apple Mac

Time Machine stores multiple copies of files and every time you change something, like a document, photo or video, it saves it as a separate version. This means that it needs much more space than a SuperDuper! backup, which is a simple clone. Ideally, a Time Machine backup drive should be at least double the size of the Mac’s internal drive.

That leaves 80 GB of unused space on the 500 GB drive. It is selected in the sidebar and Erase is clicked in the toolbar. The file format is set to MS-DOS (FAT) and the name is USB WIN. The Boot Camp partition containing Windows is just under 100 GB, but a Windows backup utility can compress backups by at least 25%, so 80 GB for the Windows backup partition is fine.

Formatting a disk partition in Disk Utility on the Apple Mac

I now have three partitions:

  1. USB SD = 150 GB for SuperDuper! backup
  2. USB TM = 270 GB for Time Machine backups
  3. USB WIN = 80 GB for Windows Boot Camp backups

Back up your Mac

Backing up with SuperDuper! is easy and I just select the Mac’s internal drive as the source and USB SD as the destination.

SuperDuper backup utility for the Apple Mac
SuperDuper! backup software for Apple Mac

Setting Time Machine to use the USB TM partition is done in System Preferences.

Select the backup drive for Time Machine on the Apple Mac
Time Machine in System Preferences

When the Mac is started in Windows from the Boot Camp partition, it cannot see the Mac partitions and only shows the FAT formatted USB WIN partition. This can then be set as the backup drive using Windows backup software.

Windows File Manager

My backups are sorted! Two Mac backups and a Windows backup means I am protected against lost files or even the whole drive. Have you sorted your backups?

In case you are wondering why the numbers don’t add up to 256 GB, the size of the Mac’s internal drive, it is because some space is used for recovery partitions, filing systems, and system files. You never get the full amount of space on a drive and you always lose a gigabyte here and there.