Types of disks you can use with Time Machine on Mac
You can use Time Machine with an AirPort Time Capsule, with a network-attached storage (NAS) device that supports Time Machine over SMB or AFP, or with an external storage device connected directly to your Mac (such as a USB or Thunderbolt drive). If a disk has partitions, you can use one of the partitions for your backup disk.
Tip: If given the choice between SMB and AFP, use SMB to back up to your external backup disk.
Time Machine can’t back up to iPhone, iPad or iPod or to a disk formatted for Windows. If you connect a disk formatted for Windows, it can be reformatted (permanently removing all data) to a Mac format and used as a backup disk.
APFS or APFS Encrypted disks are the preferred format for a Time Machine backup disk. If you select a new backup disk that’s not already formatted as an APFS disk, you get the option to erase and reformat it. If the disk is a Mac OS Extended format disk that contains an existing Time Machine backup, you aren’t asked to erase and reformat the disk.
Note: The entire APFS volume is reserved for Time Machine backups. If you want to store files other than the Time Machine backup on the same physical device, use Disk Utility to create an additional APFS volume on the disk. The two volumes then share the available space.
Time Machine still supports backups on Mac OS Extended format (Journalled), Mac OS Extended (Case-sensitive, Journalled), and Xsan formatted disks.
If the disk uses the Master Boot Record (MBR) partition type, some partitions may not be available for use with Time Machine.
If your backup disk is on a network, the network server can use Server Message Block (SMB) file sharing. Your Mac must be connected to the SMB server when you set up Time Machine. After you select the network disk in Time Machine preferences, Time Machine automatically connects to the disk when it’s time to back up or restore your data.
Note: Some network disks from manufacturers other than Apple don’t support Time Machine. If the disk doesn’t appear in the list of devices available for Time Machine backups, contact the disk’s manufacturer.