My iMac retina 4k, 21.5inch, late 2015, refuses to install Big Sur. No problem downloading, but the installation process fails after about 40 seconds, reboots, fails, reboots....... I gave up after 10 reboots, but found it looping again today having failed to auto update overnight. I have tried starting from Recovery, reinstalled Catalina, run Diagnostics with no error (ADP000), reset NVRAM, all to no avail. Anybody got any clues about this?
iMac 21.5″, macOS 10.15
Looks like you've identified the problem. There's another community thread about it here;
https://discussions.apple.com/thread/252034376?answerId=253913988022&page=1
Apparently Big Sur tries to install exclusively on the SSD part of the Fusion Drive, but during the installation demands > 40GB storage , which is then much reduced afterwards. My Fusion Drive SSD (disk0) only has 24GB:-
diskutil list
/dev/disk0 (internal, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *24.0 GB disk0
1: EFI EFI 314.6 MB disk0s1
2: Apple_APFS Container disk2 23.7 GB disk0s2
/dev/disk1 (internal, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *1.0 TB disk1
1: EFI EFI 209.7 MB disk1s1
2: Apple_APFS Container disk2 1000.0 GB disk1s2
/dev/disk2 (synthesized):
#: TYPE NAME SIZE IDENTIFIER
0: APFS Container Scheme - +1.0 TB disk2
Physical Stores disk0s2, disk1s2
1: APFS Volume Macintosh HD - Data 290.7 GB disk2s1
2: APFS Volume Preboot 86.8 MB disk2s2
3: APFS Volume Recovery 528.9 MB disk2s3
4: APFS Volume VM 3.2 GB disk2s4
5: APFS Volume Mac Built In 11.2 GB disk2s5
I don't hold out much hope of Apple fixing this for Fusion Drive 2015 iMacs because they're next in line for obsolescence :( I'm staying with Catalina!
Looks like you've identified the problem. There's another community thread about it here;
https://discussions.apple.com/thread/252034376?answerId=253913988022&page=1
Apparently Big Sur tries to install exclusively on the SSD part of the Fusion Drive, but during the installation demands > 40GB storage , which is then much reduced afterwards. My Fusion Drive SSD (disk0) only has 24GB:-
diskutil list
/dev/disk0 (internal, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *24.0 GB disk0
1: EFI EFI 314.6 MB disk0s1
2: Apple_APFS Container disk2 23.7 GB disk0s2
/dev/disk1 (internal, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *1.0 TB disk1
1: EFI EFI 209.7 MB disk1s1
2: Apple_APFS Container disk2 1000.0 GB disk1s2
/dev/disk2 (synthesized):
#: TYPE NAME SIZE IDENTIFIER
0: APFS Container Scheme - +1.0 TB disk2
Physical Stores disk0s2, disk1s2
1: APFS Volume Macintosh HD - Data 290.7 GB disk2s1
2: APFS Volume Preboot 86.8 MB disk2s2
3: APFS Volume Recovery 528.9 MB disk2s3
4: APFS Volume VM 3.2 GB disk2s4
5: APFS Volume Mac Built In 11.2 GB disk2s5
I don't hold out much hope of Apple fixing this for Fusion Drive 2015 iMacs because they're next in line for obsolescence :( I'm staying with Catalina!
I would do a Internet boot into recovery, and run Repair on your disk before installing it. Many times the install will run into corrupted files, and hang or "loop". I believe it try's to do a disk repair during the install, but the only way to truly do a repair is by booting off of another source (like internet boot or a external hard drive).
I am guessing at this point, but you may be trying to install a corrupted file. Look in the Applications folder to see if there is an installaller file there. If so, move it to the trash and try another download. Be sure to use a wired Ethernet connection, not Wi-Fi as that often results in the corruption. I hope this works for you. Good luck.
I finally got Big Sur to install. I had to clone my Catalina (Acronis True Image) to a SSD (Samsung T7), then boot from the clone, which ran noticeably faster than my Fusion Drive. I then had to erase my Fusion Drive, run "diskutil resetFusion" in Terminal and finally download and run the Big Sur Installer. It was pretty slow; I just left it installing overnight. After setting up my shiny new Big Sur, it wanted to update to 11.2.1. The install got to "About 43 seconds remaining", and hung, again overnight. In the morning it told me there was a problem, but this time it offered to send a report to Apple, and reverted back to 11.1.........
same Thing happened to me, I tried all the things mentioned in this message board, but eventually learned it’s cause of the lack of memory available on my computer. You think there would be a prompt prior to letting you go all the way. I ended up having to completely wipe my laptop and start back with Mac OS X and update several times, high Sierra, Catalina, Big sur. Definitely a pain. Before you download a good website I found was this one
https://www.google.ca/amp/s/www.iphonetricks.org/macos-big-sur-not-enough-free-space-to-upgrade/amp/
I've just tried installing big Sur using option command R. Which boots into recovery mode and gives the option of installing the latest MacOS. However, this fails with a permission denied message. I looked at the disk with the disk utility app and the disk is not writeable. This would probably explain why you can't install using recovery, and maybe why it's failing to install down the normal route. When you boot into recovery using command R which gives the option of reinstalling the installed OS (in my case Catalina) the disks are writable. All very odd.
I gave up trying to install. To get rid of the failed installer I eventually used one cloned disk as a source, booted into another external disk copy of the clone as the OS, and cloned my September 2020 clone of Catalina back on to the Mac's native disk. It worked well, but slowly because one of my clones was on a HDD. My cloning software is Acronis.
I agree that it needs to be fixed! I understand that many of your model of Mac stopped being able to update their firmware when Catalina was released. This hasn't been much of a problem until Big Sur came along. There is no known fix as of February 2021 :-(
jock_king,
No, Apple does not read or participate in these forums. They are simply our hosts. If you need to speak to Apple, please call AppleCare. If you do not know the number for your area of the planet please use the AppleCare Contact Info link to look it up.
Orthic_Thrench,
No, Apple does not read or participate in these forums. They are simply our hosts. If you need to speak to Apple, please call AppleCare. If you do not know the number for your area of the planet please use the AppleCare Contact Info link to look it up.
I was wondering if it could be some issue with the ssd component of the fusion drive not having enough space (rather than the spinning HDD). Just hope Apple are aware of the issue and planning on putting a fix in 11.3 once released!
Thanks for your reply. I've followed your suggestion, downloaded the update file over ethernet, and encountered the same reboot loop, which repeated for more than an hour without the progress bar getting past about 10%, and no "xx minutes remaining" ever being displayed. Bizarrely, I can no longer start up in Safe mode, and I have to use the Startup Manager to boot into Catalina. If I don't use the Startup Manager, the system tries to run the Big Sur installation without giving me any choice, even after I've moved the MacOS Installer to the bin and emptied the bin. I'm baffled!
I have the exact same issue except i am using an iMac Late 2015 27' (with Fusion Drive).
I was hoping that Big Sur 11.1 would rectify this issue however i end up in exactly the same loop - watching my pc try to start the installer, see a mouse cursor for 2 secs before the computer reboots, over and over again. Like you i've also ended up with an install partition i cannot get rid off and have simply select the mojave boot as the default for present.
I've tried all the advice on this forum and from Apple Support to no avail. Am hoping that this issue can be resolved soon as is very frustrating. Can only hope someone in Apple is looking at these issues and a fix will be added to a future release of Big Sur.
The really frustrating thing is that, even after I select the Catalina drive as the default, the install volume appears as the default in the Startup Manager. I don't have another Mac, so I can't try Target Disk Mode to see if the rogue startup/install volume is visible and deletable.
So not only do I get the loop. I can not even try to reinstall it because it is not recognizing my password when I hit Command R it goes to the repair screen. I select reinstall Big Sur and it does not recognize my password at all. I know it is the right password but it does not recognize it.
Big Sur Install Loop
