Updated macOS Big Sur installer resolves installation bug

in General Discussion
Apple on Monday released an updated macOS Big Sur 11.2.1 installer that properly checks for free disk space to prevent errors during the installation process.

Credit: Apple
Credit: Apple

The revision patches a critical bug in previous macOS Big Sur installers that could result in installation failure and data loss.

On Monday, Apple issued a new installer that properly checks for available disk space. If it detects that there isn't enough, it will halt the installation process and let users know how much additional space is needed. That's according to Mr. Macintosh, which first discovered the installation bug.

macOS Big Sur 11.2.1 (20D75) full installer is now available for download.

I've confirmed the new installer now checks for free space properly.

This was a serious problem, and I'm glad users will no longer get caught by this issue. https://t.co/dYSuRjdd4p pic.twitter.com/ILxoKfhORn

-- Mr. Macintosh (@ClassicII_MrMac)

The bug reportedly impacted past versions of the macOS Big Sur installer, and appears to date back to the first shipping versions of macOS Big Sur that launched in November 2020.

Because past installers failed to check for available disk space, they'd continue to run through the installation process until all available storage was exhausted. That resulted in an install loop, and possible data loss.

Macs required at least 35.5GB of free space to upgrade to macOS Big Sur, not including the 13GB installer itself.

According to Mr. Macintosh, users have been complaining about the issue since November 2020. Although there were some data recovery methods available to affected users, most had to fully erase and reinstall macOS on their machines.

The publication also appears to be the first to have alerted Apple to the issue.


  • Reply 1 of 3
    MplsPMplsP Posts: 3,268member
    Good for Apple for fixing it. It doesn't seem like it should have been that tough of a fix, so I'm surprised it took this long.
  • Reply 2 of 3
    neilmneilm Posts: 902member

    Macs required at least 35.5GB of free space to upgrade to macOS Big Sur, not including the 13GB installer itself.

    Just think about that for a minute. In round numbers you'd need 50GB of free space.

    It seems likely that many 128GB Macs would not be able to manage that. Many of the 256GB MBPs in our office wouldn't either. Hey, give people storage space and they tend to fill it.

    (And yeah, before you ask who'd bother to buy a 128GB model, one answer would be people like a teen in our family who didn't have the extra $200 for more.)
  • Reply 3 of 3
    M68000M68000 Posts: 367member
    I realize it is very complicated to develop and package Operating Systems,  but I am very surprised that they did not think of the installer doing a disk check ahead of time.  And the QA people did not think of it either?   It cannot be assumed that everyone has hundreds of gigabytes or terabytes available on their equipment.   Also,  it cannot be assumed a casual computer user would know to think about it.
    edited February 16 PetrolDave
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