#125 Remove EFI partition from MBR

open
nobody
5
2009-06-14
2009-06-14
No

Given that the EFI partition is not needed by windows/linux, would it be possible to not have it listed in the MBR (obviously leaving it in GPT), therefore allowing an extra primary partition available for an another useful partition? It would make triple booting far simpler when a separate home partition is desired.

Andrew

Discussion

  • Christoph Pfisterer

    What's listed in the MBR is not actually the EFI system partition. It is a so-called EFI Protective entry, and it covers both the GPT table itself (starting at sector 1) and the EFI system partition (starting at sector 40 usually). The MBR convention is that any sector not listed as part of a partition is considered "free". So this entry is needed to protect the GPT partition table itself from non-GPT-aware partitioning tools.

    It's possible to just remove that protective entry in the MBR, but then you'll have to be _very_ careful with any tool that touches the MBR. Because of that, I won't make it a feature in my automated tools.

    If you just want a home partition for Linux or Mac OS X, you should be able to use the fifth entry in the GPT for that. Both Linux and Mac OS X support GPT, and the home partition is not needed for booting, so it doesn't matter that it will not be listed in the MBR tables. (But you'll also want to make sure to not let any non-GPT-aware tool touch the partition tables...)

     
  • Nobody/Anonymous

    If you just want to have triple booting then you may be interested in doing the following: Via Apple software restore, copy your OSX partition on a MBR-partitioned disk. Then you can run your favourite partitioning tool, create a logical partition and as many drives as you need. No need to worry about your partition tables being out of sync. Note however: A firmware update on your Mac is only possible if you have a GPT partitioned disc.

     
  • Nobody/Anonymous

    I see what you mean about the coverage, I didn't realise it was protecting the actual gpt map as well as the (unused? but officially required) efi partition. Is there really any reason a partitioning program would ever write to these areas, especially if you've got 4 partitions defined such that there's no way anything could make new partitions?

    Yeah I had thought of trying a mbr only setup, but that would also stop me from being able to reinstall os-x directly onto the drive too, and I don't have a second mac I could easily use to make a new install image. And seeing as there was a bluetooth firmware just yesterday, and snow leopard is coming out soon, I don't want to limit myself.
    I've got a macbook, so can't easily have a second drive to boot off, I really don't want to tether myself to a usb drive permanently.

    For now, I'm just using macdrive on xp and keeping my home on the mac drive. The hfs driver in bootcamp 3.0 will make this easier if they make it r/w, the beta release is read only at the moment.

    Cheers,
    Andrew

     

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