Boot Camp erased my Mac partition. Can I recover it?
October 19, 2021 2:09 PM   Subscribe

I booted up my 2015 iMac in Windows using Bootcamp. I installed some Windows software. I did not receive any indication that anything was happening outside of my Windows partition. But when I rebooted in MacOS, I discovered that my main Mac partition was gone, replaced with a partition labeled "diskOs2". I believe I have most of the contents of my partition backed up, but if I could recover the partition whole, that would save me a lot of time. Is it possible to recover it?

Additional data points:

• I'm running Big Sur 11.6
• My mac won't mount the diskOS2. When I try, I get the following error message: "Could not mount “disk0s2”. ( error -119930868.)"

Bonus question: can you help me figure out what I did wrong in Bootcamp to make this happen? All I did was update Steam, install Virtual Desktop VR, and install the Oculus desktop software. As far as I knew, I was doing this all within the Windows partition. At no point did it ask me if I wanted to erase or rename any disks.
posted by yankeefog to Computers & Internet (8 answers total)
Response by poster: Huh. Never mind. It looks like "disk0s2" was my Mac partition, and it just wasn't mounting temporarily. I restarted a few times, and it has now mounted and seems to be fine.

So let me change the question, if that's OK: is this a warning sign of a problem that could get worse in the future? Is my hard drive on the verge of failure? And/or am I potentially putting my system at risk by booting into Boot Camp, or was it just coincidence that the problem occcurred after I had been in Windows?
posted by yankeefog at 2:28 PM on October 19, 2021

I had this issue on an older Mac (also with Bootcamp, though that might just be coincidence) and eventually it stopped being able to boot the mac partition at all. I had to put the machine into Firewire Target Disk mode (it was a very old mac) and chain it to a new machine to get the data off it.

My understanding at the time was that this was a hard drive corruption issue -- corrupt boot sectors IIRC -- and the only thing to do would have been to back up everything and replace (or at least reformat) the drive. No idea if that's what you're facing, so don't panic, but I would take the opportunity to be very sure of my backups.
posted by The Bellman at 2:40 PM on October 19, 2021 [3 favorites]

Absolutely listen to The Bellman. Don't even let your computer go to sleep or idle, make a backup immediately of everything.
posted by flimflam at 2:59 PM on October 19, 2021 [1 favorite]

Response by poster: Yikes.

Thank you, The Bellman and flimlam. That's not the answer I wanted to hear but it's extremely helpful to get it now, rather than after my hard drive died. I just checked my backups and everything seems to be in order. I'll make sure to stay on top of that for as long as my hard drive lasts.
posted by yankeefog at 3:24 AM on October 20, 2021

I'd run some drive health checks too, I'm not familiar with the latest on Macs but disk utility or fsck perhaps.
posted by Lady Li at 8:17 AM on October 20, 2021

(after you've done your backups, of course)
posted by Lady Li at 8:18 AM on October 20, 2021

If it has data that you can't live without, you'll want to create an off-computer backup of it anyway (e.g. to a cloud service or to an external drive); hardware can and will fail without warning, so assuming that your computer hardware is perpetually on the brink of death is a good mindset to have.
posted by Aleyn at 9:44 AM on October 20, 2021

Response by poster: Thanks, Lady Li and Aleyn!
posted by yankeefog at 1:29 AM on October 23, 2021

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