Re: Disk Utility repartition destroys hybrid MBR, Windows no longer boots
Re: Disk Utility repartition destroys hybrid MBR, Windows no longer boots
- Subject: Re: Disk Utility repartition destroys hybrid MBR, Windows no longer boots
- From: Thomas Tempelmann <email@hidden>
- Date: Mon, 03 Jun 2013 01:29:47 +0200
BTW, as author of iBored, a x-platform disk editor, I like to point
out some maybe lesser-known fact:
You can create a MBR for booting Windows (Bootcamp) that is listing
different partitions than what the GUID partition table (GPT) lists.
For instance, you can have 6 partitions in the GPT, yet still boot
into boot camp by listing the relevent Windows partition in the MBR.
That works because the firmware boot code looks at the MBR for booting
windows, and so that Windows, while OSX looks at the GPT, even if the
MBR is not GPT comform (the MBR of a GPT scheme should contain only
one entry, thereby pointing to the GPT).
See also this article of mine (which is a bit unfinished and chaotic,
sorry): http://www.tempel.org/WindowsWithoutBootCampAssistant
On Sun, Jun 2, 2013 at 11:54 PM, Chris Murphy <email@hidden> wrote:
> Problem ID: 11980880
>
> I'd like to call attention to this issue because whoever in engineering reported back on this bug wasn't paying attention. Many users are experiencing data loss as a result of this bug.
>
> Engineering reports:
>> This is a limitation of Windows.
>
>
> It's not. It's a limitation of BIOS/MBR. If Windows were installed on UEFI/GPT the problem wouldn't occur.
>
>>
>>
>> Adding a extra HFS partition will break windows.
>
> Because when adding that 5th partition, Disk Utility nukes the hybrid MBR, replaces it with a protective MBR, and therefore there isn't a Windows entry in the partition table. Disk Utility behavior in this scenario directly leads to data loss.
>
>> We can not prevent this.
>
> Yes you can. Don't allow users to create a 5th partition when there is a hybrid MBR.
>
> I cite this Apple technote:
> http://developer.apple.com/library/mac/#technotes/tn2166/_index.html
>
> Please see the 2nd paragraph under the Protective MBR heading. Disk Utility is a GPT aware program, LBA 0 contains an "other form" of MBR, a hybrid MBR, Disk Utility should "refuse to manipulate the disk" per this technote. Yet Disk Utility isn't following Apple's own technote guildeline in this scenario. Further it says "manipulating the GPT may cause dangerous inconsistencies between it and the legacy MBR". How about that, the user experiences data loss as a result of adding a 5th partition, just as the Technote predicts.
>
> Thank you.
>
> Chris Murphy
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--
Thomas Tempelmann, http://www.tempel.org/
Follow me on Twitter: http://twitter.com/#!/tempelorg
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