Several of you have recently asked whether Time Machine (TM) is best for making backups, or whether you’d be better off using a third-party backup utility. While I can’t compare them, here’s a list of what I consider to be TM’s strengths and its weaknesses, when running in Sonoma and backing up to APFS.

Strengths

Interface. TM has a relatively uncomplicated interface in System Settings and the Time Machine app. Many users like the illusion created by that app, although as it’s also well integrated into the Finder, you can choose which you prefer.

Backup frequency. TM was originally designed to make small backups every hour, and that’s still the best way to use it, even though in Sonoma you can opt for daily or weekly backups instead. This ensures that working documents that may change a great deal over the course of a few hours will have hourly backups you can return to.

Inclusions and exclusions. TM incorporates a standard list of items excluded from its backups, such as volume version databases, and provides a simple method of adding custom exclusions in its settings. Default behaviour includes the automatic exclusion of volumes on external storage, which can always be added back when desired.

Dispatch. For such frequent backups, they have to be dispatched so they can be run in the background while you’re still working. TM accomplishes this as a background task scheduled and dispatched by the DAS-CTS system so that their impact is minimised. In Apple silicon Macs, backing up is performed using the Efficiency cores, allowing user apps to continue running at full speed on Performance cores, and for energy efficiency.

Snapshots and versions. TM’s hourly backups are accompanied by local snapshots providing another layer of safety. Document versions, snapshots and backups are also well integrated into many apps and the Time Machine app itself.

Backup storage. TM supports automatic rotation of multiple backup storage, allowing you to keep separate backup sets on different drives with a minimum of fuss.

Backup determination. TM can use any of a range of different strategies to determine what needs to be backed up, including the use of FSEvents when available, and snapshot deltas. The most efficient is chosen automatically, without user intervention.

Backup content support. TM has full support for APFS special file types such as sparse files, and performs block copying as much as possible to minimise the amount of data that needs to be copied, and the space required in backup storage. When working with large files, this leads to substantial savings in time and space.

Backup integrity. TM’s synthetic snapshots are read-only and can’t be modified, preventing other apps from tampering with them.

Backup maintenance. TM automatically thins its backups on both a time and space basis, ensuring that they use a minimum of storage space.

Restore integration. TM backups are well integrated with Migration Assistant for the purpose of restoring Data volumes.

Command tool. The tmutil command tool gives access to an extended range of features for advanced use.

Weaknesses

Backup plans. Although TM is flexible enough to cope with missing source volumes and backup storage, and will make snapshots alone when no backup storage is available, it has a single backup plan or regime. You can’t set up two or more backup scripts.

New frequencies unproven. The new daily and weekly backup options in Sonoma are relatively unproven.

Small files. TM doesn’t back up large numbers of small files at all well. It remains unsuitable for backing up some commonplace apps, such as Xcode, as a result.

Speed. TM’s file transfers incur I/O throttling even when that Mac isn’t otherwise in use, and that slows transfer rates when making backups, particularly when made over a network.

Integrity checks. There’s no current way to check the integrity of file data within TM backups.

Backup immobility. It’s not currently possible for users to copy or move TM backups, because of their snapshot format. While this may be possible using the asr command tool, even advanced users struggle with this.

Logs. TM’s logs are written to the Unified log, making them harder to access, and the diagnosis of problems considerably more difficult.

Documentation. That for users is limited, and there is essentially no technical documentation.

General restrictions

Some of TM’s current limitations aren’t specific to it, but more general, and likely to apply to all similar backup utilities.

Local files only. When backing up files that are also kept in cloud storage, including iCloud Drive, only files that have been downloaded (materialised) locally can be backed up. This applies to all backup utilities.

No System or snapshots. TM cannot make a copy, clone or backup of the active System volume, nor of any snapshots, including the macOS SSV.

If you can think of any more, please add them in comments.