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. Macintosh, Big Sur still has a serious issue that could lead to data loss when users try to upgrade a Mac to the latest version of the operating system without enough free space.
After noticing several reports from users online, Mr. Macintosh found that the MacOS Big Sur installer does not check if the Mac’s internal storage has enough free space. When the system starts the update process, the Mac does not respond and data may be permanently corrupted.
Apple says upgrading to macOS Big Sur for the first time requires at least 35.5 GB of available storage ̵
The update process seems to be running perfectly, but users will receive the following message near the end of the installation:
An error occurred while preparing the software update.
From that point on, the Mac will no longer boot. Mr. Macintosh was able to confirm that this error 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 (for example, updating from macOS 11.1 to macOS 11.2).
If you have a backup of your data, you can simply delete the entire disk and reinstall macOS. However, it can be very difficult to restore data without backup.
When FileVault is enabled, you need to connect your Mac to another Mac via target disk mode to recover your files. If FileVault was not enabled on your Mac, you can try deleting some files using the Terminal app in macOS Recovery, which allows macOS to complete the update process.
Apple has not commented on this bug so far, but hopefully it will be fixed with the final release of macOS Big Sur 11.3. You can read more information about this issue at Mr. Macintosh blog.
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