Last Week on My Mac: Squeezing a thimbleful of update into a ten-gallon can

Updating macOS has never been more painful and fraught than in Big Sur. What had previously been a periodic distraction has changed in the last eight months into an unreliable and inefficient mess, which all too often consumes time when I can least afford it.

The whole objective of updates is that they should be unobtrusive procedures which minimise download time and user inconvenience. In Catalina and earlier, Apple provided ordinary users with three main choices:

  • online delta updates delivered through Software Update and softwareupdate to individual Macs;
  • offline standalone delta and combo updates available to download;
  • locally cached delta updates from the Content Caching Server.

Without any warning – in fact, with Apple claiming that Big Sur would make macOS updates “faster” and “easier than ever” – Apple removed the second of those options, and short of downloading and installing the whole of Big Sur, users now have only two choices for updates:

  • online delta updates delivered through Software Update and softwareupdate to individual Macs;
  • locally cached partial delta updates from Content Caching Server.

What Apple also didn’t warn us of was that Big Sur’s updates have become inefficient to the point of absurdity. Last weeks’ security patch was an excellent example, in that it brought one small but very important fix for a bug, which didn’t apparently require a new kernel, firmware revision, or any discernible changes in the build or version numbers of the contents of /System/Library. Yet for M1 Macs it required the download of over 3 GB, fifteen minutes ‘preparation’, and a further 20-30 minutes to install.

Even if you’ve followed Apple’s advice and set up a Content Caching Server, each M1 Mac to be updated requires just under 1 GB of that update to be freshly downloaded direct from Apple’s servers rather than the local cache. The end result is that in its brief cycle, Big Sur has broken Apple’s previous records for requiring the largest quantity of updates: my chart below shows how macOS 11 has already required a total of over 31 GB of updates on Intel models, and more than 43 GB on M1 models.


In 11.5.1, Apple has succeeded in squeezing a thimbleful of a patch into a ten-gallon can of update, more than 99% of which is overhead. To compound that, those ten-gallon updates often don’t even work properly, forcing the user to download a full installer, weighing in at around 13 GB, and consuming even more time.

This has currently happened to my M1 Mac mini. It updated happily to 11.5, and remains stuck there. The Software Update pane in 11.5 is apparently unable to find any update for it, although it’s now five days since 11.5.1 was released. My only option therefore is to download the full 11.5.1 installer app, and hope that can connect with my existing Data volume. Neither am I the only Big Sur user who appears unable to update successfully to 11.5.1: several have contacted me to ask what they can do when 11.5 or older versions simply stop updating correctly. Where’s the standalone installer, they ask, but it’s a question Apple refuses to answer.

The upshot is that more and more users are giving up the battle to keep Big Sur up to date. My M1 mini won’t ever get to 11.5.1, as I’ll simply leave it until Monterey is released and upgrade to that, leaving it vulnerable to a bug which is already being exploited in the wild, for at least two months. Once your system updates start encouraging users to take such risks, you know that you’ve got them badly wrong.

This is perhaps best illustrated in the ‘total cost of ownership’ (TCO) for the first year of each recent version of macOS. This is simply the sum of the size of the initial installer, plus the size of all system updates during the year in which that version of macOS was current:

  • macOS Mojave 10.14 = 26.7 GB
  • macOS Catalina 10.15 = 37.1 GB
  • macOS Big Sur 11, Intel = 43.7 GB
  • macOS Big Sur 11, M1 = 66.6 GB.

If those aren’t enough to convince you of Big Sur’s problem, consider its future. Over the next two years, it’s expected to receive maintenance. Traditionally, that should mean six or seven Security Updates each year. Even if each is a minimum size of 3.1 GB (for an M1 Mac), that would add a further 40 GB or so to the TCO, bringing it to more than 100 GB – or 0.1 TB – during its supported lifetime. How many thimblefuls is that?