Mac Practice: The Silent Failure of Time Machine – and How to Prevent Data Loss | News

Backups are only good if they happen regularly. To achieve this, Apple’s Time Machine has some clever functions: Every hour, a routine in the background saves all changes to a second storage medium. After a week, Time Machine automatically cleans up and reduces the number of individual saves to one per day; after a month it is evaporated to weekly save levels. In order not to scare users away with incomprehensible messages, Time Machine is very reserved when it comes to error messages – perhaps even too reserved: Howard Oakley observed that Time Machine did not back up data for nine months. Nothing in macOS actively pointed this out to him.

The problem arose when testing security software that verifies external devices – it regulates access to peripherals on desktop Macs similar to data protection & security/accessories on mobile Macs. After installing it, the previously connected Time Machine drive was still registered in the Finder; apparently the mounted APFS volumes remained available. It wasn’t until the next day that he discovered by chance that Finder only seemed to continue to have access to the external drive. He only became aware of it when he clicked on the symbol in the menu bar. After he deactivated the tested software and thus restored access to the SSD, Time Machine started working without comment. MacOS apparently didn’t think it was worth mentioning that no data was backed up for 16 hours.

When does Time Machine warn?
It is unclear when macOS 26 (Tahoe) indicates the failure of a data backup. When Time Machine was introduced, a notice appeared every ten days that no backup copies had been created. The comments suggest that Time Machine only indicates after 30 days that no backups are being saved externally. This can quickly lead to a serious data failure: macOS creates hourly snapshots in order to write them to the backup when the Time Machine volume comes into contact. However, if the data volume is defective, all intermediate statuses will be lost. Users have no influence on this: Neither the dialog under Settings/General/Time Machine nor the command line tool tmutil allow querying or changing the warning interval. Users therefore have to actively look for the icon in the menu bar to find out when the last successful backup was completed.

Time Machine’s settings dialog only allows you to set the backup frequency and excluded folders.

Remedy only from third-party providers?
Notifying the user of every failed backup via a message would certainly be overkill – especially with mobile Macs. But macOS could indicate failed backups earlier, especially on stationary computers. At least one setting option would be helpful. macOS also does not offer a desktop widget for the Time Machine status. The Backup Status app, which costs €4.99, retrofits this for macOS 14 or newer, but has not been updated for two years. If you want more control over data backup, you should look for alternatives like Carbon Copy Cloner.