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How to Access a Virtual Partition from WinPE 

Jul 08, 2008 04:44 PM

GSS 2.5 has a different mechanism to create/handle virtual partition. Previous to GSS 2.5, virtual partition is added to existing partition table as an overlapping partition. So if there is no free slot in partition table (i.e. 4 primary partitions are already used), GSS can't create a virtual partition.

With GSS 2.5, GSS is replacing the mbr rather than editing the existing mbr. When virtual partition is created, GSS saves existing mbr to osmbr.bak file and replace the mbr with virtual partition mbr.

Restore an existing mbr

When the machine boot to WinPE, there will be only virtual partition from mbr. At this moment, users can't access existing partitions.

Once GSS copies all necessary files from virtual partition to WinPE ramdisk, GSS runs the following command to revert back to original mbr.

gdisk32 /revert

From this moment, users will see original partitions without virtual partition.

Advantages

There are a few advantages of this method:

  • GSS can create a virtual partition even there is no free slot in the partition table
  • There is no overlapping partition so other programs will work better. e.g. diskpart
  • Users will see exactly the same partition layout as before. No additional partition to existing partition layout.

How to access virtual partition

All above operation is defined in start.bat file and it will run automatically. So once users have access to WinPE, virtual partition is not available from mbr. Users can only access existing partitions.

If you want to access virtual partition again, you have to replace the existing mbr with virtual partition mbr. this can be done using gdisk32 and virtual partition mbr file. Which is in WinPE ramdisk. (i.e. x:\ghost directory)

Run the following command to access virtual partition.

gdisk32 [disk number] /mbr /replace:vpmbr.bin

After this, you can access virtual partition again. Remember that when you run the above command, you can't access existing partitions, you can only access virtual partition. If you want to copy files from virtual partition, you can copy it to ramdisk first and later you can copy it to the existing partitions.

How to access existing partitions again

There are two ways to restore existing partitions:

  • One way is to use gdisk32 /revert command line.
  • The other way is to use osmbr.bak file with the following command line.
    gdisk32 [disk number] /mbr /replace:osmbr.bak
    
    

The later command line can be useful in the following scenario...

After creating a virtual partition with WinPE, the machine will fail to boot to WinPE. Such as blue screen of death. In this case, you can boot the machine with other media(e.g. pxe, cd ... etc) and grab osmbr.bak file. Normally this file is available in the root directory of the OS partition.

Once you get this file, you can restore the original mbr so the machine will be bootable again.

Conclusion

It is good that users now don't have to worry about virtual partition. They will see no change after booting into WinPE. They will see exactly the same partition layout as before. However, there might be some cases that users want to access virtual partition. In this case, they can use above method to enable/disable virtual partition.

If there are any questions or you need clarification, please add a comment!

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