The trouble with things that just work is that when they stop working, you’re often not aware that anything is amiss. Time Machine is like that: extremely popular, a huge advance in ensuring that Mac users back up, but it can so readily go wrong. When it does, I’m afraid that a lot of users only discover that weeks later, when they need to recover data using a backup that was never made, or was broken.
This is particularly true for laptop users who are much of the time away from their backup drive. Although Time Machine makes local backups then, if your hard drive goes down, or your laptop goes missing, you may find that its last external backup was a couple of months ago, and of little use.
The quickest way to know that Time Machine has been backing up is to enable its presence in the menu bar, and glance at that: that should tell you when the last backup occurred, but nothing else.
To get more detail, open the Time Machine pane in System Preferences. In between making backups, this will tell you:
- the amount of free space available on your backup drive,
- the date of the oldest backup on that drive,
- the time of the last backup which was attempted
- the approximate time that the next attempt to backup will start.
As I have reported, Time Machine in Sierra can sometimes make backups at irregular intervals, as if on demand, rather than hourly. I do not understand how or why that occurs, but it can.
Whilst you’ve got this pane open, check the Options, as those are important and can sometimes become changed without your being aware.
The important item here is the list of items which are to be excluded from backups. Check this carefully, as any files in those locations will not be recoverable from your backup.
If you want to make a new backup, from scratch, as you might when changing your backup drive, one important question is how much space would the first, full backup take. The answer is given here: assuming that you keep the same exclusion list, that full backup would here require just short of 1 TB.
If you open the Time Machine pane whilst a backup is in progress, you are given quite different information:
- the amount of free space available on your backup drive (as before),
- a progress bar indicating the proportion of the current backup which has been completed,
- a numeric account, stating the stage of backing up (e.g. preparing), and if backing up is in progress, the amount of the backup complete,
- an estimate of the time remaining to complete that backup.
The last is valuable if you want to shut your Mac down, for example.
If Time Machine does not complete a backup successfully, you should be shown an alert informing you of that. Unfortunately, its message is often not particularly helpful, it is not completely reliable (backups can sometimes fail silently), and we often click through without paying sufficient attention.
If you want to check your Time Machine backups in more detail, the best way in Sierra is using LogLogger5, as detailed here. In El Capitan and earlier, you can open Console and filter on backup or Time Machine, and browse messages. In Sierra, Console cannot do that retrospectively, but LogLogger5 can, and does so more easily.
You should also periodically – every few weeks – check that you can restore at least one document and a folder of files from your Time Machine backup. If you don’t check this, you could later discover that many of your backups are missing, which would be bad news when you desperately need them.
Time Machine is not easy to fix when it does become broken. If you have errors which you cannot fix, the best source of information about Time Machine and what you can do to fix problems is the late James Pond’s Time Machine Tips. Although it has not been updated since 2013, when he died, it is still a unique resource, and we hope someone will be able to take it on and maintain it in the future.