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I have a hybrid disk. After trying to copy some files from another disk to this one, I lost my OSX and Ubuntu boot capability. Ran gptsync and got:

Current GPT partition table:
 #      Start LBA      End LBA  Type
 1             34         1987  BIOS Boot Partition
 2           1988   1029662719  Basic Data
 3     1029662720   2108995583  Basic Data
 4     2108995584   2109405183  EFI System (FAT)
 5     2109405184   2517004287  Mac OS X HFS+
 6     2517266432   2667417599  Mac OS X HFS+
 7     2667417600   3900229631  Basic Data
 8     3900230504   3907029118  Linux Swap

Current MBR partition table:
 # A    Start LBA      End LBA  Type
 1              1   3907029167  ee  EFI Protective

Status: MBR table must be updated.

Proposed new MBR partition table:
 # A    Start LBA      End LBA  Type
 1              1           33  ee  EFI Protective
 2             34         1987  da  Non-FS data
 3           1988   1029662719  83  Linux
 4 *   1029662720   2108995583  07  NTFS/HPFS

May I update the MBR as printed above? [y/N] 

Clearly the MBR table is damaged or mismatched. But it does not reflect the correct GPT table partitions at all. How do I get the MBR repaired to match the GPT table (up to the 4 part limit of course)?

The question is simply - Do I blindly say Yes to gptsync's suggestion? It looks sort of ok but not exactly so...Advice please on interpreting the above output to get my disk usable would be greatly appreciated.

Thank You!

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1 Answer 1

Technically, no hybrid MBR is OK; hybrid MBRs are a clear violation of the GPT specification. Whoever invented them should be ashamed of him/herself. Unfortunately, they're a practical necessity for dual-booting OS X and Windows on Macs. (That may change with Windows 8, though.)

That said, within the usual informal rules for a hybrid MBR, the one that gptsync is suggesting is OK. My suspicion is you think it's not OK because the first partition (of type "ee") doesn't match any of your GPT partitions. This is not only fine, it's necessary; the type-0xEE partition is the protective partition, which is required to identify the disk as a GPT disk. It's not really a partition definition, in the sense that it does not point to an area of the disk that can be used to hold filesystems or whatnot. On a standards-compliant GPT disk, this partition spans the entire disk (except for the MBR itself) and exists to keep GPT-unaware tools from messing with the disk. On a hybrid MBR, this partition is reduced in size, often dramatically, and up to three "real" GPT partitions are added to the MBR table.

As to whether you should accept this partition table, I'm not sure; that depends on what partitions Windows needs to be able to access. If Windows only needs to access /dev/sda3 (in GPT; /dev/sda4 in the proposed hybrid MBR), then it should work OK as-is. If Windows needs to access any later partition(s), though, you may need to get more creative. You can do this with gdisk (part of the gdisk package in Ubuntu) by using the h option on the recovery & transformation menu. The details appear in the gdisk Web-based documentation.

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