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How can I remove MBR from external HD?


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#1 AlfredSka

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Posted 15 December 2007 - 08:40

Updated to be clear about what I'm trying to achieve (original post at bottom):

I want to remove boot information from the MBR of an external hard drive:
1) Currently, the external hard drive has GRUB written to MBR
2) The partitions on the external hard drive are new, and did not exist when GRUB was installed to the MBR
3) I would like to erase only GRUB's boot information from the MBR while keeping the partitions intact
4) The partitions, in order are 40GB FAT32, 500GB NTFS, 120GB EXT3. They are all storage volumes, no OS.
5) Right now, if I try to boot from USB, this drive is seen and GRUB tries to load. GRUB then fails since there is no longer an OS on this drive.
6) If I tell the computer to boot from USB, I would like the computer to skip over this drive, rather then trying to boot it.

Thanks,
Matt

________________OLD ORIGINAL POST BELOW________________
I have an external hard drive (connecting via USB) with three partitions, 1FAT32, 1NTFS, 1EXT3. I need to erase GRUB from the MBR, but can't figure out how to do it. I don't want to replace it with another boot manager, in fact that's the problem, I need the drive to NOT be bootable. I've long since erased the linux partition that installed GRUB in the first place, and this is strictly a storage volume now.

I have Windows Vista and Ubuntu set up on my computer, so if you know of any tools I can use under either OS, it'd be appreciated. I also have XP on a virtual machine.

~Matt

Edited by AlfredSka, 15 December 2007 - 21:53.



#2 panicswitched

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Posted 15 December 2007 - 09:42

format the drive or sometimes in windows you can unset the drive as active

#3 +accesser

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Posted 15 December 2007 - 09:53

try the windows CMD command
fdisk /mbr
http://support.microsoft.com/kb/69013

Only thing is I’m not sure if this will work over USB

#4 panicswitched

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Posted 15 December 2007 - 10:00

accesser thats only for the main drive and that will restore the mbr but only on the active drive not anything else

The fdisk /mbr command only re-writes the MBR on the system drive (DISK-0) using BIOS calls. You cannot specify any other drive for the fdisk /mbr command to operate on other than DISK-0.



#5 +BudMan

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Posted 15 December 2007 - 16:45

Um if you wipe the MBR -- then there would be no partitions on your disk

http://en.wikipedia....ter_Boot_Record

If the disk is partition, then it would have a MBR. I think what your looking to do is just remove the Boot Flag from one of the partitions -- not remove the MBR itself.

Any number of partitions tools would be able to remove the boot flag/active flag from a partition for you. Or overwrite the MBR with just your partition details, etc.. The above link gives you about everything you would need/want to know about the MBR ;)

#6 OP AlfredSka

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Posted 15 December 2007 - 18:39

It sounds like I need to explain a bit more:

1) ALL partitions were deleted before these partitions were created. Realize, the boot record is not written over by simply deleting partitions. None of the partitions have a boot flag. For proof, I've attached a screenshot of gparted:
Posted Image

2) I don't want the drive to boot ANYTHING. Essentially, if I have several devices hooked up to the computer at boot time, and I tell the computer to boot from USB, I want it to skip over this drive (and not consider it an option).

#7 OP AlfredSka

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Posted 15 December 2007 - 18:56

Here's some more information:

I found Roadkil's Sector editor which shows GRUB occupying the boot sector:

Posted Image
Posted Image

It looks like it's occupying sectors 0-17. I've never used a utility like this before. Would it be safe to write zeros to these sectors? Or would that delete information about my partitions as well?

#8 Eric

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Posted 15 December 2007 - 19:04

If you use a WinPE disk, you can use DISKPART and use the CLEAN command in it to completely wipe all tables from the drive. If you decide to do so, be VERY careful as DISKPART has no safety features. :)

(If you're using Vista, I think the install disc has it too. Just boot from it and open a command prompt.)

#9 +BudMan

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Posted 15 December 2007 - 19:17

Here is the tool your looking for.

http://www.diydatare....nl/mbrtool.htm
http://www.diydatare...tool_manual.htm

MBRtool allows you to do the following things:

* backup, verify and restore the MBR, using backup-sectors or files
* backup, restore, wipe, clean or dump the track 0 for a disk
* edit or wipe the MBR Partition Table
* refresh the MBR bootcode, without destroying the Volume Bytes
* remove the MBR bootcode
* re-write the MBR signature bytes
* display the MBR sector or dump the MBR sector to file
* perform above mentioned edit, bootcode, display and dump functions on the MBR backups
* create a blank backup-file to create a MBR from scratch and restore it later
* perform attribute changes on partitions listed in the MBR Partition Table (hide, activate, delete etc.)
* manipulate the volume bytes that are associated with volumes in Windows NT / 2K / XP

You do not want to remove the MBR which contains where your partitions are -- you just want to remove the Grub Bootloader code.. Which is exactly what this tool will allow you to do.

#10 OP AlfredSka

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Posted 15 December 2007 - 20:52

Here is the tool your looking for.

http://www.diydatare....nl/mbrtool.htm
http://www.diydatare...tool_manual.htm


MBRtool sounded promising, but alas it's not going to work for me.

I'm running a laptop, so the drive must remain on an external USB port. Unfortunately, MBRtool does not read USB drives. (I even used a ghost boot disc with USB support (UHCI.exe) to boot, then ran mbrtool without success.) MBRtool sees my laptop's hard drive just fine, but not anything on USB.

I'm suspecting there is a single hex key that I can change in the boot sector to say (Not Bootable), but I need to figure out for sure which it is.

EDIT: I'm currently looking into MBRwizard (http://www.mbrwizard.com/) and will report results.

Edited by AlfredSka, 15 December 2007 - 21:17.


#11 OP AlfredSka

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Posted 15 December 2007 - 22:09

EDIT: I'm currently looking into MBRwizard (http://www.mbrwizard.com/) and will report results.


I tried MBRWiz, but issuing
mbrwiz /disk=1 /wipe=mbr
also wiped my partition table. I've restored the backup MBR, and I'm back to where I started. Any ideas of other tools that would work under windows? Or does someone know which key/sector I can change to specify non-bootable?

#12 OP AlfredSka

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Posted 16 December 2007 - 01:44

I found partial success by following the directions here: http://www.cyberciti...uninstall-grub/

I used the linux method, which did get rid of GRUB, but my computer's boot sequence still can't get past the drive.
I also used the lilo method from the comments of that page, but encountered similar results.

In either case my partition table remained intact.

#13 JimmyM

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Posted 23 December 2007 - 06:56

I tried MBRWiz, but issuing

mbrwiz /disk=1 /wipe=mbr
also wiped my partition table. I've restored the backup MBR, and I'm back to where I started. Any ideas of other tools that would work under windows? Or does someone know which key/sector I can change to specify non-bootable?


Try the following
mbrwiz /disk=1 /repair=1
this will replace the current MBR boot code with a standard Windows XP MBR, effectively overwriting any existing GRUB loader code. Also, this option leaves the partition table untouched!