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Windows 7: Benefits of GPT vs MBR Primary and MBR Logical Partitions ?

17 Feb 2014   #21
SIW2

Microsoft Community Contributor Award Recipient

Vista x64 / 7 X64
 
 

This whole efi/gpt thing certainly adds complexity and introduces limitations for the end user. They don't get much choice, pretty much all the new laptops the average Joe buys come like that now.


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17 Feb 2014   #22
jumanji

Windows 7 Home Premium 32 bit
 
 

.......and therefore it will be wiser for anyone with GPT drives to save all the important sectors using Bootice so that one can restore the drive to the original condition in case partition related problems arise making the drive inaccessible.

The screenshot below shows a GPT drive with three partitions.

Benefits of GPT vs MBR Primary and MBR Logical Partitions ?-17-02-2014-21-56-51.jpg

In this case as an example, I would save LBA0(sector 0), LBA1, LBA2, LBA34, and then the three NTFS volume boot records LBA 262178, LBA 366634632 and LBA 732818343.

During the restoration process I would start with restoring the backups that are supposed to exist in the last sector (LBA n) and LBA n-32. These might have gotten corrupted and need to be restored first.

So I would restore the last sector n with the GPT header - saved LBA1, and then sector n-32 with the GPT Table - saved LBA2.

EDIT: The following figure shows the partition structure of a GPT drive.

Benefits of GPT vs MBR Primary and MBR Logical Partitions ?-18-02-2014-10-58-37.jpg

That should give an idea what all sectors one should backup and save. That would depend upon the number of GPT partitions one has. While restoring the saved sectors to the backup area in the drive the following progression should be maintained.

LBA n (the last sector) with saved LBA 1 and then on LBA n-32 with saved LBA 2, LBA n-31 with saved LBA 3, LBA n-30 with saved LBA4 .......... upto LBA n-1 with saved LBA 33

Then LBA 0, 1, 2,.......to 34 and other VBRs with the respective saves.

In most cases, one should be back in business and be able to access the drives as before without the necessity of trying any data recovery software the efficacy of which in dealing with GPT drives, in my view, is uncertain as on date.

On how to save and restore the sectors using Bootice, Lost partitions!

Update: Amplified in post#29 to be read in conjunction with.


My System SpecsSystem Spec
17 Feb 2014   #23
SIW2

Microsoft Community Contributor Award Recipient

Vista x64 / 7 X64
 
 

Far,far,far too complicated for the average user.
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17 Feb 2014   #24
jumanji

Windows 7 Home Premium 32 bit
 
 

I am an average user , honestly. ( looks, reads very complicated but once you do it you know you can do it and if I can do it then anyone can.)
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17 Feb 2014   #25
milindsmart

Windows 7 Home Premium x64
 
 

I think this is the KB article in question : Disk drive numbers may not correspond to the SATA channel numbers when you install Windows on a computer that has multiple SATA or RAID disks
My goodness... What an atrocious error! This is absolutely mind-blowing in stupidity. Drive numbering according to.... order of enumeration.
Even with this brain-dead manner of drive numbering, how could it get confused with ITS own numbering in a SINGLE boot!?

And yeah, the tool is apparently buggy, if it can't find the simple truth that this disk was GPT.
But wait, could you not tell it that this was a GPT disk, and so not to try to interpret it as MBR?
Perhaps your classification of partition managers as Beta is right... It's so much easier to recover from GPT, I can only blame the tool.Reassigning GUID is trivial. simply replacing with a protective MBR would have let any other tool recover the backup partition table.

Windows is to blame for getting confused, but Lazesoft is to blame for not recognizing the basic GPT layout. There is NO 3mb partition connected with GPT at all. Wonder what it scanned...
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17 Feb 2014   #26
milindsmart

Windows 7 Home Premium x64
 
 

SIW2, What do you think of this idea of mine?
gpt - Out of Band Disk Partitioning and Tables - Super User

Would like some super-expert opinions
My System SpecsSystem Spec
17 Feb 2014   #27
mjf

Windows 7x64 Home Premium SP1
 
 

As I've said the vast majority of users don't need a GPT boot disk (really useful on a 250GB SSD!). However, as SIW2 says it's pretty much standard on most bought PCs so if you are interested in computers it is probably worth understanding the GPT standard.
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17 Feb 2014   #28
alan10

Windows 7 Ultimate 64 bit SP1 x64
 
 

Quote   Quote: Originally Posted by milindsmart View Post
I think this is the KB article in question : Disk drive numbers may not correspond to the SATA channel numbers when you install Windows on a computer that has multiple SATA or RAID disks
My goodness... What an atrocious error! This is absolutely mind-blowing in stupidity. Drive numbering according to.... order of enumeration.
Even with this brain-dead manner of drive numbering, how could it get confused with ITS own numbering in a SINGLE boot!?
I totally agree.

Quote:
Windows is to blame for getting confused, but Lazesoft is to blame for not recognizing the basic GPT layout. There is NO 3mb partition connected with GPT at all. Wonder what it scanned...
I remembered wrongly, and Lazesoft made absolutely no such mistake.

I actually tried many third party tools and they were all defeated by Windows insisting that the GPT DIsk had to retain the MBR style of Disk Identity.
Perhaps I could have booted into a LINUX Recovery tool and fixed the problem,
but I thought it more likely that Learning to use Linux tools would result in me placing everything in jeopardy.

It was the commercial MINIDISK DATA RECOVERY which showed me 3 MB things which I assumed were remnants of GPT links.

Lazesoft actually showed me 1.41 MB EFISECTORS, which I assume are your GPT linked list.
Lazesoft was NOT being used to recover partitions but was digging through UNALLOCATED SPACE in that region of the disc, and it did the job perfectly.
It rescued over 400 GB of Macrium Partition Image backup files,
and Macrium has validated all the internal checksums of each file,
THEREFORE all the fragments were correctly assembled (the files were fragmented when first created).

The only alternative data recovery that recovered each file with the correct number of bytes,
probably assumed that no file was fragmented,and simply located the start sector for each file and then read a contiguous set of sectors, actually composing a "recovered file" which consisted of fragments of many different files. Macrium tested its recovery attempts and each one failed hash checksum validation.

Lazesoft now has a recently enhanced capability to repair in a few minutes all the damage done by Windows when Windows "converted" the GPT disk into a trashed MBR disk,
BUT I will only test this once I am satisfied that I have NOT RECOVERED ANY FILES that I actually deleted BEFORE Windows has trashed the system.

Regards
Alan


Attached Thumbnails
Benefits of GPT vs MBR Primary and MBR Logical Partitions ?-sshot-97.png   Benefits of GPT vs MBR Primary and MBR Logical Partitions ?-sshot-151.png  
My System SpecsSystem Spec
18 Feb 2014   #29
jumanji

Windows 7 Home Premium 32 bit
 
 

Having gone through all the posts in this thread this morning and having noted that Windows can create problems by not enumerating the disks in the same order with each startup and presenting a different picture to the unwary user, I am more than ever convinced that users with GPT drives will be better off saving the important sectors in all the drives they use - whether MBR or GPT.

In the case of MBR disks the screenshot below shows the typical LBAs one would save for later restoration. (This disk has three primary and three logical drives.)

Benefits of GPT vs MBR Primary and MBR Logical Partitions ?-18-02-2014-15-39-34.jpg

I have since amplified my post #22 by including a figure showing the GPT structure. I repeat it here with some colours added.

Benefits of GPT vs MBR Primary and MBR Logical Partitions ?-arrow.jpg

On a GPT drive if one has 128 partitions then one may have to save roughly 38+128(VBR) LBAs.

But considering that nobody is likely to have more than 12 partitions the number of LBA saves get reduced to 6+12(VBR) LBAs. Each sector save is only 512bytes.

And saving the LBAs with Bootice is not at all a difficult task. One just selects the drive, clicks on Sector Edit, view the partition details, select the sectors one by one and click on the save to file icon. Similar process for restoring. ( In the case of restoring the sectors on the system drive that has gone awry one may have to perhaps run Bootice from a WinPE disk or remove the HDD and place it as a second drive on another system and run Bootice). By default Bootice saves the files in the same folder in which it resides.

The only problem an average user will face is what goes where when restoring. The GPT structure figure coupled with the text statements should come in handy for that. Does not take much time to figure out and understand.

If anyone who wants to undertake this exercise face any problem, we are always here to walk you through.


My System SpecsSystem Spec
18 Feb 2014   #30
mjf

Windows 7x64 Home Premium SP1
 
 

The enumeration sata port issue has been raised here many times before. I lean towards a BIOS explanation as proposed here:
Diskpart / Disk Management vs the BIOS
Now does a UEFI BIOS solve this --- who knows. But for all practical purposes it may not matter.
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 Benefits of GPT vs MBR Primary and MBR Logical Partitions ?




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