"Boot OS X" partition

Discussion in 'macOS' started by oMc, Jun 7, 2018.

  1. oMc macrumors 6502

    oMc

    Joined:
    Oct 17, 2010
    Location:
    Finland & France
    #1
    Hi,

    So, I recently had an issue with my MacBook and I had to restore from my Time Machine backup (High Sierra, 10.13.5). The issue was that I tried to upgrade my internal SSD to APFS, but wasn't able to boot anymore from the main partition after the conversion.

    The thing is that, since the restoration, I don't have a recovery partition anymore. Instead, I have a partition named "Boot OS X" (see attached screenshot). I cannot find a lot of info about this partition on the web, but some people say that it may be associated with Time Machine (see here). It has the same size as the recovery partition used to have (650 Mo).

    Capture d'écran 2018-06-07 23.37.49.png

    I have also noticed that when I start the computer and hold option, I obviously don't have the recovery partition as a choice to boot from, but instead, I can boot from "MacBook" (disk0s2) or the Time Machine itself. When I do so, I go straight to the same menu as the recovery mode (Disk Utility, Restore from TM, Install Mac OS, etc...). When the Time Machine is turned off or unplugged, holding option during boot does nothing and the MacBook just boot normally (as, I guess, there is no other choice than the "MacBook" partition anyway).

    I am a bit confused. Is it possible that this Boot OS X partition was created during the TM restoration as some sort of replacement to the Recovery HD? It is weird because it seems to act as a recovery partition but requires the TM to be plugged in and turned on to be able to boot from it.

    I just want to add that the Mac is running fine and everything since the restoration, and that I don't mind that much about lacking a proper Recovery partition (I have a bootable USB with High Sierra anyway). I just want to understand what is that Boot OS X partition :)

    Thanks!
    oMc
     
  2. casperes1996 macrumors 68040

    casperes1996

    Joined:
    Jan 26, 2014
    Location:
    Horsens, Denmark
    #2
    If my understanding is correct, Boot OS X helps to boot from otherwise unsupported booting setups. For instance, if you have a Fusion Drive, Boot OS X will reside on the SSD to instruct the system at boot time as to how to proceed with the boot-up procedure, given that the Fusion Drive is a single disk , but the OS probably only resides on the SSD, and the pre-boot environment doesn't have the Core Storage drivers to read the Fusion Drive without the Boot partition.

    In the case of your APFS conversion it is likely to ensure that the firmware can boot up an APFS volume, even if the firmware doesn't natively support APFS, by giving an APFS driver in a special partition; Boot OS X.
     
  3. oMc thread starter macrumors 6502

    oMc

    Joined:
    Oct 17, 2010
    Location:
    Finland & France
    #3
    Thanks. The thing is that the APFS conversion didn’t work and since the TM restoration I’m back to HFS+. So, is it so that this Boot OS X partition is some kind of leftover of the unsuccessful APFS conversion?

    If so, how can I safely get rid of it via the terminal and how?
    --- Post Merged, Jun 7, 2018 ---
    Sorry for the double post.

    Apparently, I should be able to delete this "disk0s3" partition and reclaim the space by using the terminal and the "erase" and "merge" commands of diskutil. I will probably try it tomorrow.
     
  4. casperes1996 macrumors 68040

    casperes1996

    Joined:
    Jan 26, 2014
    Location:
    Horsens, Denmark
    #4

    A lot better, but still not quite a Retina generation iMac. - That one will at least run the latest operating system bound to be released this fall, but is also the earliest model that will get official support. It's also not a Retina model. The retinas are the one with 4k or 5k screens (4k for 21" and 5K for 27")
    Like this one:
    https://www.amazon.co.uk/Apple-Reti...2034&sr=8-3&keywords=refurbished+5k+2015+iMac

    PS. Haven't checked for better value deals at all.
     
  5. oMc thread starter macrumors 6502

    oMc

    Joined:
    Oct 17, 2010
    Location:
    Finland & France
    #5
    You replied to the wrong topic I believe ;)
     
  6. DeltaMac macrumors G3

    DeltaMac

    Joined:
    Jul 30, 2003
    Location:
    Delaware
    #6
    The Recovery system is not usually in the Option-boot chooser screen. The normal method to boot to Recovery System is by restarting while holding Command-r
    But, a full restore through time machine likely just left you with a restored drive, but without the recovery system itself. Apparently, then you need the Time Machine backup attached to boot to that. Just how Time Machine functions, I suppose.
    If you really want to recreate the normal recovery system partition - http://osxdaily.com/2016/07/03/recreate-recovery-partition-mac/
     
  7. casperes1996 macrumors 68040

    casperes1996

    Joined:
    Jan 26, 2014
    Location:
    Horsens, Denmark
    #7

    Huh? That was from an entirely different thread. I wonder what happened that made me reply to a different thread in this thread..... I'm confused now.
    Thanks for catching it though
     
  8. oMc thread starter macrumors 6502

    oMc

    Joined:
    Oct 17, 2010
    Location:
    Finland & France
    #8
    Oh yeah, you're right, I totally forgot about that. In any case, when I booted with Command+R, the Mac went straight to the internet recovery mode, suggesting that no proper Recovery HD was present on my SSD.

    Anyway, I failed to delete this "Boot OS X" partition using the terminal and diskutil, some error related to the partition map showed up. The disk partition was also returning errors when trying to repair with Disk Utility.

    So I booted using my High Sierra USB key, made sure to erase the whole disk properly this time, and then restored my most recent Time Machine. Now, the recovery HD is showing up in the list of partition:

    Capture d'écran 2018-06-08 20.26.03.png

    I believe that, when I restored in the first place after the APFS conversion failed, I did not formatted completely the SSD, leaving behind some leftovers of the failed conversion.
     

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