Catalina has brought an increase in problems reported with Time Machine backups. Unlike some backup utilities, Time Machine seldom provides actionable information when it gets into trouble. To find out what is wrong with it, you’ll normally need another utility which can guide you to a diagnosis. This article suggests which utility to use for some of the most common symptoms.

These utilities – T2M2, Ulbow, Consolation and Mints – are all free from their Product Page.

Are you letting Time Machine run its normal automatic backups, or are you using a third-party tool to schedule them?

Third-party apps which take control of Time Machine do so by disabling its normal scheduling mechanism, replacing it with their own. In the course of doing so, the log entries made by Time Machine have different identifiers, and aren’t detected or analysed by T2M2, or using the standard filters in Consolation, Ulbow or Mints.

To analyse their problems, you’ll need to use Ulbow or Consolation with custom filters set to detect their log entries. You may be able to identify those by viewing the whole log from the start of one of their backups.

If you’re using normal scheduled backups in Time Machine, then T2M2, Ulbow, Consolation and Mints should all be able to see relevant log entries for those backups. If they can’t, see here.

Have automatic backups stopped altogether, or become very irregular?

When Time Machine isn’t making a backup, run T2M2 to check the last few hours of backups. It should tell you how irregular those backups have been, and whether this is because the macOS scheduling system has stopped working properly. For futher details, see this article.

If that doesn’t help, use the Time Machine log browser in Mints, which displays all the relevant log entries for you.

Are you seeing errors during a backup?

When Time Machine isn’t making a backup, run T2M2 to check the last backup or two. Most significant errors should then be listed in its report, but that doesn’t include some classes of error which can normally be safely disregarded. To get fuller detail from all of the sub-systems involved, use the Time Machine log browser in Mints, which displays all relevant log entries.

Is your first or subsequent backup taking forever?

This is a common problem in Catalina, with many potential causes. T2M2 now has a Check Speed button which is designed to diagnose this, as detailed here. Further details of what you can do to deal with this are explained here. If you want to use Ulbow’s chart feature to investigate this, that’s described here.

Does Time Machine keep making full backups every time?

This requires careful checking of the full log as provided by Mints, against a normal record such as that shown here. Pay particular attention to the initial location of the backup store and the data to be backed up, the strategy selected to decide what needs backing up, and any errors which occur before the transfer of files takes place.

Is Time Machine repeatedly backing up very large files such as a Virtual Machine?

This article explains how to avoid this wasting much of your disk space.

List of current articles which could help:

Time Machine: 1 How it works, or fails to
Time Machine: 2 What it writes in the log
Time Machine: 3 Analysing automatic backups
Time Machine: 4 Problems with backups
Time Machine: 5 Changing Macs and more
Time Machine: 6 Networked storage
Time Machine: 7 Checking logs using Ulbow
Time Machine: 8 Preventing problems
Time Machine: 9 Inside backup support files
Time Machine: 10 Tools
Time Machine: 11 tmutil
Time Machine 12: Backups that never complete
Time Machine 13: Backups and versions
Time Machine 14: Diagnosing and working around slow backups
Checking backup transfer rates using T2M2 version 1.13
Time Machine 15: Large files including VMs
Time Machine 16: Reading a normal backup in Catalina using Mints
How to check the integrity of files in a Time Machine backup
What to do when T2M2 or another log-based app returns an error