clean install Big Sur in Recovery mode without data loss?

[jk73]

If I’m running low on HD space but need to reinstall Big Sur ***without data loss,*** is it as simple as booting into Recovery mode, erasing “Macintosh HD” (but NOT “Macintosh HD - Data”), and then reinstalling Big Sur from the Recovery menu, or is this wishful thinking?

I stupidly let my HD get too full and, of course, I have my first corrupted system in years.

Thanks for all feedback.

(Posting from my iPad.)

 

[mikzn]

I stupidly let my HD get too full and, of course, I have my first corrupted system in years.

Before you start reinstalling, have you tried the storage management tool in the "About this Mac" menu? see screen shot below

Often there are some large video files or other media that can be moved to an external drive? I like to keep about 30% of my drive clear for best performance.

It is possible that your OS is not corrupted and just acting strange due to being too full?

 

[Honza1]

I stupidly let my HD get too full and, of course, I have my first corrupted system in years.

Corrupted system files OR corrupted SSD drive structure OR simply too full?

If too full, see above.

If SSD drive structure is corrupted: proceed VERY carefully. You should first make sure you have good backup. Even if drive is corrupted, it is sometimes possible to copy data away from the drive and make backup. If needed you can try to use target mode from another mac (if available). After you get good backup (and test it) try to repair it, if that doe snot work, try to reformat completely and reinstall. And if even that fails (it did to me), it may be SSD failure which requires mainboard replacement. Either way, external backup (or two) of the data is critical here!

I would be surprised if you had “Macintosh HD” files corrupted. The whole reason of this drive is that it is mounted read only during regular user runtime. It cannot be changed, unless you are installing system upgrade. If you had failure during system upgrade, then it is possible, I guess. But other that that, it is unlikely.
So all "corruptible" data are on your “Macintosh HD - Data” - including your own private configuration data. Principally, you should be able to delete the Data drive and system should just create a new one. Of course, that user looses all data.

 

[jk73]

Thanks for the replies. Not sure if I have one or multiple issues.

As mentioned above, I foolishly let my HD space get down to about 20 GB free. Last night, I was working in Safari with a lot of tabs open and Safari suddenly crashed with a “your system ran out of memory” error. After that, I noticed I was down to 4 GB free, which seemed very strange. My system otherwise seemed to be operating okay, but I figured a restart was a good idea. That’s where the real trouble started.

Upon restarting, booting fails at about 20% into the progress bar, then crashes with a “your computer restarted because of an error” message. This loops multiple times until it stops and shows a URL to Apple Support for Mac startup issues.

The MBP will not launch into Safe Mode but it launches into Recovery Mode. There, disk utility fails on my Macintosh HD and Macintosh HD - Data volumes with the following errors and messages:

object map is invalid

problem -69842 occurred while restoring the original mount state"

file system check exit code is 8

Disk utility shows only 4 GB free, so it looks like there’s a huge cache eating up my HD and/or some other type of corruption or failure occurred.

I‘ve been hoping to hold out for a 2021 16-inch MBP, but those seem a ways off.

My main concern is saving the data from the past few days. My last backup was about a week ago, but there are a few documents from this week I’m hoping to recover.

All feedback appreciated.

 

[mikzn]

I think it would help if you provided how much total internal storage you have? 128gb, 500gb, 1TB?

Also what model of Mac? is the SSD upgradable?

The more specific info you provide the better / more relevant advice forum members here can provide

I had similar issues about a year ago because my Photos library grew to almost 120g - moving the photos library to an external was an instant fix and performance boost

 

[jk73]

500 GB. Everything was working fine until the weird Safari crash last night, which somehow chewed up ~15 GB of space.

 

[Honza1]

This looks bad.
It may have been different sequence - something chewed up the 15GB and That caused Safari to crash... Difficult to say, these SSD supposedly behave poorly when they are over 80% full. No experience myself with that.
Depending on what Mac model you have you can try to mount it in target mode (if you have another compatible mac and appropriate cable). Check Apple for instructions, but basically it lets you mount your mac drive as external drive to another mac. IF the drive mounts, you can try to copy home folder to some other medium.
Apple gurus/phone support might help, but reports here are that their solution is (bit too often) wipe, install new copy of system, restore from backup... They automatically assume, that you have hourly backup (TimeMachine), which you obviously do not have.
If the mac has upgradable SSD (= you can remove it), you could try to extract it and use external enclosure on different mac and see, if it mounts there. In that case, as desperate move, you could remove the MacintoshHD, which would give you some breathing space on drive. Reinstall of system is always possible...
My personal experience with fixing the APFS structure has been poor. And there is big IF on mounting the drive. Disk utility clearly has issues.
Good luck, you will need it.

 

[BLUEDOG314]

Can you run 'diskutil apfs list' in terminal from recovery and post results here. If you get a bunch of nonsense for the size of the apfs container and volumes within you are going to need to erase everything after attempting data recovery with something like target disk mode mentioned above. At this point if the system thinks it only has 4GB free space it is probably not even going to let you install the OS again without erasing and throw up some error about not enough free space.

 

[jk73]

Thanks for the replies. The MBP boots into Target Disk Mode but I can’t get any other MBP to recognize it. Disk Drill, however, is able to see, as far as I can tell, all of my files, so I’m hoping to recover them tomorrow and then try to make the MBP bootable again.

I’ll try the suggestions above tomorrow. I’ve been wanting to save my files before trying to delete Macintosh HD and reinstalling, since the possibility of data loss apparently exists (?).

I tried the “Reinstall macOS” option while in Recovery mode, but it indeed failed because of a lack of space. The error says 31 GB is required for a Big Sur installation.

Thanks again.

 

[Honza1]

I’ll try the suggestions above tomorrow. I’ve been wanting to save my files before trying to delete Macintosh HD and reinstalling, since the possibility of data loss apparently exists (?).

ANY time you boot a computer, tiny chance of data loss exists. This chance increases A LOT when you start messing up with system (upgrades, reinstallations, ...). It increases even more, when you are in situation as you are. My suggestion here is to backup, test the backup is readable and usable - AND COMPLETE. And then, just to be sure, make separate second backup and check that. And only after that risk trying to do system surgery you are planning to do. Chance of data loss in your situation is quite high, may be 50/50. Disk utility is reporting some structural error on your disk...

 

[jk73]

Thanks for the reply. I definitely want to achieve a full backup before trying to get the old MBP bootable again. Somehow, I ended up with a too-full HD and no individual external drive big enough to copy the whole HD at one time. (I have photos and videos on one USB, and everything else on another, but the last backup was about a week before the issue arose.)

Does CarbonCopyCloner work in Recovery Mode in Big Sur? That is, if I buy a 1 TB external HD, format it with a bootable CCC/Big Sur disk image, and then boot my old MBP from this new external HD, should CCC be able to see my files and create a backup? I was able to install Disk Drill via Terminal and it was quickly able to see all of my files, so I assume CCC would be able to, but I‘m not sure. Thanks.

 

[Honza1]

Does CarbonCopyCloner work in Recovery Mode in Big Sur? That is, if I buy a 1 TB external HD, format it with a bootable CCC/Big Sur disk image, and then boot my old MBP from this new external HD, should CCC be able to see my files and create a backup? I was able to install Disk Drill via Terminal and it was quickly able to see all of my files, so I assume CCC would be able to, but I‘m not sure. Thanks.

AFAIK CCC needs regular system running, so you cannot run it from Recovery mode. You might be able to mount the disk using Target mode to another mac and run CCC on that mac to clone the disk to external enclosure. But it may still be challenge, my understanding is, that making bootable clone is either not possible or marginally possible in Big Sur. Reports vary and I do not have experience myself. Reports are complicated since now we have intel macs (better chance) and M1 macs (less chance) to deal with, so it is bit of mess...
What I would do is get external drive, mount somehow existing disk - in target mode or in recovery if possible - together with the external disk and copy as much as possible of "Data" drive to it. Ideally all. In Finder or using better tools (if in Target mode) or using command line if in recovery. Once the data are copied and tested that they are accessible, I would try to delete some data from "Data" drive and see, if that would let system boot or at least reinstall. There has to be a lot of junk data somewhere there. Or delete folder with something I have good backup of - music, photos, some large stuff - and see if that liberates enough space. May be delete any snapshots which may be where lots of space is hiding...

If not, I would boot in internet recovery, reformat the drive clean, test if structure is now OK, instal new system and then try to run Migration assistant to move my data back from backup. If it works, great, if not, move data manually and reinstall applications.

Anything above will take time, can nuke the data or whole SSD and in general, is pain to do. Good luck.

 

[jk73]

Thanks for the detailed reply. I now have a 2 TB external HD, so I’m ready to attempt a full backup.

As a first attempt, how does using Disk Utility in Recovery Mode to make and transfer a full disk image of “Macintosh HD - Data” sound? Thanks again.

 

[Honza1]

As a first attempt, how does using Disk Utility in Recovery Mode to make and transfer a full disk image of “Macintosh HD - Data” sound? Thanks again.

Do not have personal experience. If it works, great. Let us know, please. Good luck.

 

[jk73]

Do not have personal experience. If it works, great. Let us know, please. Good luck.

Unfortunately, Disk Utility did not work, except for a couple of very small folders. Trying to create a disk image for any folder bigger than 1 GB failed with a disk error.

I bought a 2 TB external HD, installed Big Sur on it, booted my ailing MBP from it, and then Carbon Copy Cloner copied the entire MBP (450 GB), except for six photos that had been corrupted, like a champ. (Trying to copy large folders via Finder repeatedly failed with “device error.”) Awesome app.