MacOS Big Sur upgrade causing data loss if low on drive space


MacOS Big Sur Upgrade Causing Data Loss if low on drive space

MacOS Big Sur

MacOS Big Sur was reportedly causing data loss if low on drive space when upgraded.

The Installers fail to check available drive space before they try to upgrade.

Mac owners who wants to upgrade to the macOS Big Sur should be very careful if they notice that they are running low on drive space, as in this case, the happening could reportedly lead to data loss.

The main issue here is that an initial upgrade to Big Sur requires more space, a minimum of about 35.5GB to be available on the drive, plus another 13GB for the macOS Big Sur installer itself (making a total of 48.5GB). If you don’t have that much space available, then things can go badly wrong, as reported by Mr Macintosh.

The issue is that apparently macOS doesn’t know or check if you have that amount of drive space before it is starting the installation process, and when the installer subsequently runs out of space, some other people are reporting getting an “error occurred preparing the software update” message.

The Mac now becomes stuck in the Boot Recovery Assistant environment, having no way to recover. Well, there is no easy or obvious way to recover, anyway, leaving the data on the disk in danger of being lost – more on that in a moment.

Do Note that this isn’t affecting those users that are upgrading to a different point release of macOS Big Sur – like, from version 11.1 to 11.2 – but it is affecting those using the full installers to upgrade their machines direct to either Big Sur 11.2, or the beta of Big Sur 11.3.

Sticky Situation

The possible solution for recovery procedure depends on the exact scenario you’re sticker in, as explained in the blog post by Mr Macintosh, but if you have got FileVault encryption enabled on your system, things can get very sticky.

Indeed, in the case later, the only avenue to go about righting your system and also recovering your data is by using a 2nd Mac (running macOS High Sierra or Mojave) and connecting the two machines up. So, many people will have difficulty there , as it isn’t exactly that common to have more than one Mac (or easy to borrow one, if you don’t).

The easiest course of action for some people may simply be by starting from scratch, choosing to erase and to reinstall macOS; providing that they have an up-to-date backup, and won’t lose data that way.

Apple has not acknowledged the bug yet, and as mentioned it is still very present in the beta of the Big Sur 11.3 – but hopefully now it has been highlighted in a major way, the Mac maker will be looking and working on the issue (if it isn’t already under investigation). We’ve contacted Apple for a comment and probably a way out on this matter, and will update this story if we get any back. 

As you may have noticed, macOS Big Sur 11.2 was only recently deployed, delivering some important fixes including a solution for the Bluetooth problems which have been disturbing some M1-powered Mac owners.