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backup OEM OS or recovery partition for future reinstallation


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But.. if the system cannot find the duplicate GTP, what does it do? Do you mean that it doesn't simply recreate it from the first copy automatically?  :thumbdown

 

Hard to say. :unsure:

 

The (did I say stupid) EFI/UEFI/GPT specifications (just like any other specification) are about how things should be, not how an OS should react if anything is not as it should be according to the specifications.

 

The generic idea of a "second copy" of something is that it should be used if the first copy is not good, but, although a GPT partition entry does have a "verify hash" that should (or could) be used to detect data corruption in the entry itself, it is just a self-referencing check (useful, but not foolproof) which leaves us with the fact that if the first copy is not good (though valid regarding the hash), there is no real way to know if not by comparing with the "second copy", if the first copy is actually different from the second copy and the OS would automatically update the second copy to reflect the content of the first one the whole idea of the second copy as a "reference" would be m00t. :( 

 

To give you an example of a similar mechanism (but opposite), the FAT have usually two copies that may go "out of sync" (for whatever reasons) and you usually need to run a specialized program to fix the issue or, more commonly, a NTFS volume on a partitioned device has (outside the volume but inside the partition) a copy of first sector of the bootsector.

In case the second copy of the bootsector is missing or corrupt running CHKDSK will - if I recall it correctly - recreate it but windows will boot (or the volume will be mounted) normally.

In case the first copy of the bootsector is missing or corrupt windows won't boot (or the volume won't be mounted) normally, still there is not (and it's a good thing that there isn't) an automatic mechanism to fix the first copy and you will need to restore manually from the second copy or use (say) TESTDISK to the same effect.

 

But in that case it is a "plain" backup or "emergency provision", a NTFS volume on a non-partitioned device (super-floppy) has NOT the second copy.

 

It is entirely possible that someone has read the specifications in such a way that an OS *needs* both copies of the partition entries. :ph34r:

 

Actually (though I have never experienced the issue Tripredacus reports) it is only too logic that a "sensible" OS when finding something that is not exactly as it should be would throw an error of some kind, I was only pointing out what definitely cannot be achieved by a "RAW" copy restored to a media with a different number of sectors in the case of a "GPT style" disk, it is possible that the issue reported comes from *something else*.

 

jaclaz

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