MacOS Big Sur was officially released to all users in November last year, and since then Apple has released updates with bug fixes and general improvements. However, as reported by Mr. MacintoshBig Sur still has a serious problem that can result in data loss when users try to upgrade a Mac to the latest version of the operating system without enough available space.
After seeing several user reports on the web, Mr. Macintosh I found that the macOS Big Sur installer is not checking that the Mac’s internal storage has enough free space. As the system starts the update process, the Mac stops responding and data can be permanently corrupted.
Apple says upgrading to macOS Big Sur for the first time requires at least 35.5 GB of available storage – and that does not include the 13 GB macOS Big Sur installer. Unfortunately, even if your Mac doesn’t have 35.5 GB of available storage, macOS will try to install the Big Sur update, which is when users can lose all of their data.
The update process seems to work perfectly, but users receive the following message near the end of the installation:
An error occurred while preparing the software update.
From that point, the Mac will no longer boot. Mr. Macintosh was able to confirm that this bug affects the macOS Big Sur 11.2 installer and even the macOS Big Sur 11.3 beta installer. At the same time, this does not affect OTA updates from one Big Sur installation to another (such as upgrading from macOS 11.1 to macOS 11.2).
If you have a backup of your data, you can simply erase the entire disk and reinstall macOS. However, recovering data without backup can be very difficult.
With FileVault enabled, you must connect your Mac to another Mac using the target disk mode to recover your files. If FileVault is not enabled on your Mac, you can try to delete some files using the Terminal application in macOS Recovery, which will allow macOS to complete the update process successfully.
Apple has not commented on this bug so far, but hopefully it will be fixed with the final version of macOS Big Sur 11.3. You can read more details about this problem at Mr. Macintosh blog.
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