Apple has released an updated macOS Big Sur installer bringing the software to version 11.2.1. This version of the installer can correctly check for available free disk space to prevent errors during the installation process. The update is a patch for a critical bug in previous installers for Big Sur that could result in installation failure and data loss.
The updated installer checks for available disk space, and if it detects there isn’t enough space, the installation process is stopped. In that instance, users are given a message that lets them know how much additional space is needed. The fix was confirmed by a Twitter user known as Mr. Macintosh, who was reportedly the first to discover the bug.
Before the bug was patched, the installer failed to check if the required 35 gigabytes of drive space was available before beginning the installation. If there wasn’t enough free space, or if FV2 was enabled, the installation of Big Sur would fail, and data on the computer was inaccessible. The same user has confirmed the new installer checks for free space properly and will prompt you if too little free space is available.
The original bug impacted versions of the macOS Big Sur installer back to the first shipping version of the operating system in November 2020. Because those initial installers failed to check for available disk space, the installation process ran until available space was consumed. That resulted in an install loop and possible data loss.
Mac computers need at least 35.5 gigabytes of free space to update to Big Sur in addition to enough room for the 13-gigabyte installer. Data recovery methods are available to help affected users, but some had to fully erase and reinstall the operating system on their Mac computers.