[Cialug] Partition table gone

[Tom Pohl]

I use the utility named testdisk on the recovery is possible live cd  
(rip linux)

I've had great success finding paritions on both windows and mac  
partitioned disks.

-Tom


On Feb 21, 2009, at 1:09 PM, "Daniel A. Ramaley" <daniel.ramaley at drake.edu 
 > wrote:

> I've started reading about GPT and agree that if only overwriting the
> first 512 bytes it *seems* the drive should still work. I've verified
> that only the first 512 bytes were zeroed. In a hex editor i can see
> that bytes 0x00 to 0x1FF are all 0, and that at 0x200 "EFI PART"
> appears, marking the beginning of the actual partition table.
>
> I did have rEFIt installed on the OS X partition. I don't know if that
> changes things drastically, but i should have mentioned it in my first
> message.
>
> Right now i'm making a copy of the disk onto another machine by way of
> dd and ssh. Once that's done, i'm going to start trying to recover.  
> One
> idea i've had would be to boot an OS X DVD and repartition the drive  
> as
> it was before, and then install OS X as i had it. Then i'd know that
> the beginning of the drive was in a consistent state. I know what  
> block
> numbers the partition boundaries are on, so once i had things back  
> to a
> consistent state, i could use dd to copy the actual partition data  
> from
> the backup i'm making. I *think* that would get things back. I'm not
> worried about recovering the Ubuntu installation as i didn't have
> anything important on there and can just reinstall.
>
> If you think taking the first 512 bytes from another disk and slapping
> it onto the front of my disk would fix the problem, that would
> certainly be faster than my idea. I'd be willing to give it a try if
> you can send me those magic 512 bytes.
>
> On Saturday February 21 2009, Zachary Kotlarek wrote:
>> On EFI machines, the first LBA, including the traditional primary
>> partition table, is not actually used -- it's just there so machines/
>> software that don't know about GPT (GUID Partition Table) don't see
>> the disk as empty. So if you really only overwrote the first 512  
>> bytes
>>   I would not expect you to have and trouble with the disk, at least
>> not on a machine that actually reads GPT disks.
>>
>> That being said, if you think having the first LBA restored would  
>> help
>>   things I can send you a copy of one from an Intel Mac. Probably
>> even one with a 320 GB disk.
>>
>> If you did blow away the partition table from the beginning of the
>> disk (maybe you overwrote the first 512 blocks instead of bytes) you
>> can restore it from the backup at the end of the disk -- it's written
>>   to both ends. Note that while the partition entries are stored in
>> the same order on both ends, the header is the first and last LBA on
>> the disk (sans the fake MBR in LBA0), so you need to copy in two
>> distinct segments.
>>
>> OS X provides a gpt command-line tool, which I suspect is on the
>> install disk. You could use it, or any other GPT-aware formatting  
>> tool
>>   that does not try to initialize volumes, to manually restore the
>> table. Assuming you know the exact size and location of each
>> partition of course.
>> x-man-page://8/gpt
>>
>> Basic GPT references:
>> http://en.wikipedia.org/wiki/GUID_Partition_Table
>> http://developer.apple.com/technotes/tn2006/tn2166.html
>
> --- 
> ---------------------------------------------------------------------
> Dan Ramaley                            Dial Center 118, Drake  
> University
> Network Programmer/Analyst             2407 Carpenter Ave
> +1 515 271-4540                        Des Moines IA 50311 USA
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