1 Topic by jmcc

  • jmcc
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Topic: Manually edit pointer of the boot sector backup location?

Hi, Thanks for the great work with GParted.

I have an issue with a disk and was wondering if there was a manual method to repair in order to understand a bit better.

It is an NTFS disk and after a resize operation the copy of the boot sector which is supposed to be on the last sector of the volume isn't there.

It seems that older versions of NTFS placed the backup boot sector in the middle of the disk rather than at the end.

It should be simple to manually copy the boot sector contents to an arbitrary empty sector on the disk, and this could become the new backup boot sector.

I am wondering though, how to edit the pointer or reference to look at the new arbitrary sector for the backup instead of the last sector of the volume where the backup is usually found. 

At what offset is this pointer located? Can it be edited so the backup boot sector can be placed anywhere on the disk? Any advice would be very appreciated.

2 Reply by class413

  • class413
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Re: Manually edit pointer of the boot sector backup location?

As far as I know, master boot sector backup isn't a standard feature of the MBR system. It is a standard for the GPT system (the backup is located in the last Mib of the drive space, however I don't think it is directly accessible by the user).
The FAT filesystem keeps its file table at the beginning of the partition and the mirror copy of this table just after.

The various solutions for the MBR backup copy come usually from programs and aren't standardized. I remember that such an old program kept backup of the sector 0 (MBR) in the sector 1 of the drive, that was free because the first partition start was the sector 63.

Furthermore, the MBR backup isn't related to the NTFS or any other filesystem in the partitions. If the partition table is broken, the windows system can't repair it.
The NTFS filesystem keeps backup of the Master file tables (MFT) of the system. These tables are kept in a position around the 1/3 of the partition/volume space, but I don't know if this is valid for multi-drive volumes.

Concerning the partition boot sector, there is a duplicate somewhere on the drive, according to this page, however the offset isn't specified.  Perhaps it is related to the  commercial recovery program that supports that web page.

*** It is highly recommended to backup any important files before doing resize/move operations. ***