Mac’s Time Machine seems to work so slickly that we may be lulled into a false sense of security
I admit that I used to assume that, once it had backed up a file, Time Machine would keep it – at least until it had to remove some old backups to make way for newer ones.
A few days ago, though, one of my IT Support clients specifically asked me whether Time Machine still keeps files deleted from the main drive, so I started doing some digging. Apple don’t seem to offer any technical information at all on exactly what the software does – this is all I could find on the subject.
The nearest I’ve come to anything that sounds in any way authoritative on the subject is from Király’s comments on this Apple discussion page. In Király’s opinion, Time Machine appears arbitrarily to decide which daily backup to retain as a weekly backup and it appears that no attempt is made by Time Machine to ensure that all the different files created and amended during the week are preserved in the weekly backup. So, if you created a file on Monday and then worked on it on Tuesday and Wednesday, it would be in the daily backups for those days. But if you then deleted it and Time Machine chose to carry the Friday daily backup forward as the weekly backup then the backup of the file worked on earlier in the week would be lost. Presumably, the same would apply when deciding which weekly backup is retained to become the monthly backup.
I haven’t found anything else that precisely confirms this situation, but neither have I found anything that denies it. However, I did come across a more detailed critique of Time Machine at the Mac Observer. While not addressing my specific concern of deleted files not being kept in the backups, it does express other concerns about Time Machine.
So, assuming that (like me) you no longer have complete faith in Time Machine, what do you do?
Well, I don’t recommend abandoning Time Machine just because of this. It’s easy to set up and it seems to work well for most situations. Instead, I recommend taking manual backups of important files and folders as often as you feel it is worth it. So if, for example, you have a folder of important work that occupies, say, 10gb, and that folder contains files that are regularly changed and added to, then I would invest in 3 X 16gb USB flash drives (about £5 each from Ryman) and periodically copy the entire folder to one of those drives and rotate the drives that you use. It’s important when doing this to add the files to the USB drive without deleting the previous contents of the USB drive first. Otherwise, you are, once again, in danger of losing files that are no longer on the hard drive. If you are talking about large music or photo collections, then you might have to use external hard drives instead of USB flash drives.
Alternatively, you could “archive” huge chunks of the data that never change and only back up the more volatile files. Personally, I take “archive” copies of important folders periodically as well as my regular backups. Archive copies are ones that are never deleted or overwritten. So, if you take an archive copy onto DVDRs (not the rewritable DVDRWs) then you know you have a copy as long as the DVD is readable (we might expect this to be forever but see my blog on data retention). Many laptops nowadays do not have inbuilt CD/DVD players, but you can buy external ones that connect by USB cable when you need them (see my blog on external CD/DVD drives). Of course, DVDs can normally only contain about 4gb of data, so this strategy has its limitations.
Another possibility to consider is creating backups and/or archives onto SD cards. I currently take daily backups of my important folders onto a 128gb SD card (that I never bother removing from the machine). Since this is a separate drive from the internal (SSD) drive, it gives me some protection against SSD drive failure.
The concept of backups is easy. It just means making copies of things so that you are not left bereft if something happens to the original. In practice, though, it can become very complicated. As a general principle, I would always recommend that backups of important things are taken in more than one way, onto more than one medium, at more than one time, and kept in more than one place. And it now appears to me that that principle holds good even if your primary backup method on a Mac is Time Machine.
By the way, did you know that 31st March is “World Backup Day“? I kid you not. Who decides these things? What happens if two different “causes” want the same day?