Your 2 TB Time Machine drive is half empty: using the rest for files without breaking backups

A 2 TB drive for backing up a 512 GB Mac is more space than Time Machine needs. It would also like to use every byte of it, because it keeps older backups until the drive is full. If you want to keep films or old projects on the same drive, give Time Machine its own space.

Two ways to share one drive

Method 1: a second APFS volume (no erasing)

An APFS drive is a container that can hold several volumes sharing the same free space. Adding a volume for files is instant and does not touch the backups.

1. Open Disk Utility and choose View, Show All Devices.
2. Select the Time Machine volume on the external drive.
3. Click the + button in the toolbar, labelled Add APFS Volume.
4. Name it, for example Files, and click Size Options.
5. Set a Quota on the backup volume instead if you want, so Time Machine cannot take everything.

The simpler way to cap backups is a reserve size on the Files volume, which guarantees it that much space. Anything left over is shared.

Method 2: a separate partition

If the new part needs to work on Windows, it must be a separate partition in ExFAT. In Disk Utility select the drive at the top level, click Partition, then +, and choose ExFAT. On an APFS drive Disk Utility can often do this without erasing, but not always, so copy anything important off first.

How big should the backup part be?

A common rule is two to three times the space used on your Mac. That gives Time Machine room for months of history. Check what you use now:

df -h /System/Volumes/Data

# Time Machine's own view of its backups
tmutil listbackups 2>/dev/null | tail -3

If the backup drive is already full, see Time Machine backup drive full.