MBR and Track 0

I normally make a regular, full backup of a disk with two primary and one logical partition. Restore offers a choice of restoring MBR and track 0 if I just restore a single partition, rather than the whole disk. Why wuld I want to restore MBR, and how will I know if I need to?

 

By coincidence I used Restore MBR and Track 0 this morning because I had a problem. I thought I was going to have to restore the whole hardrive but was pleasantly surprised to see the option of just restoring the MBR. In seconds the hardrive was back as it was. Brilliant.
John

 

The MBR contains the Master Boot Code, the Disk Signature and the Partition Table. The Master Boot Code scans the disk for the Active partition and loads a copy of the boot sector, from that partition into RAM. The Disk Signature is not associated with a specific physical disk, which means that Disk Signature can be copied between physical disks. The Partition Table is the most significant item of information because if the disk geometry differs from the Partition Table the disk will in all probability not boot or may boot with errors.

1. When to restore the MBR

If your System Disk fails to boot, it could be because the MBR is corrupt. Instead of restoring the entire disk you could try to restore just the MBR and see if that resolved the problem.

2. When NOT to restore the MBR

Let us assume that at the time of making your most recent images your disk had 2 partitions - System and Data and you made 2 separate images. The System image will contain the disk MBR because it is the Active partition. The Partition Table within the MBR of that image will contain information relevant to the disk (2 partitions, Partition Label, Partition Size, Start Sector...etc )

Let us further assume that since making that image you re-partitioned your disk into 3 partitions - System, MyData and MyMedia. Windows will have rewritten the Partition Table within the MBR of the disk to reflect this new geometry and information.

Now, for some reason, you have a problem with, for example, Windows, and you want to restore your latest image of the System partition. In this case you would NOT restore the MBR because the MBR in the image will contain the old Partition Table information which does not reflect the new geometry of the disk.

 

Many thanks for that helpful reply. I was wondering about the same thing.

That's where I get a little confused. Is the MBR part of the system partition? If so, restoring the system partition also restores the incorrect MBR.

OTOH, if the MBR is separate from the system partition, then restoring without the MBR will overwrite the damaged system partition with the imaged system partition, leaving the (correct) MBR unchanged.

 

No, the MBR is not part of the System partition. Any Primary partition on a disk that contains an Operating System can be assigned to be the Active partition.

The MBR is ALWAYS located at Sector-1, Cylinder-0, Head-0 of the disk. Within the MBR is the Master Boot Code which scans the disk for the Active partition and boots whatever OS is contained within that partition. The only requirements are that a) it is a Primary partition, b) is is marked Active and c) it contains an OS.

Therefore, if you restore only the System partition you do not restore the MBR. This is the principal reason why Acronis provide you with the option to restore the MBR and the System partition separately.

BEFORE you restore the MBR always make sure that the MBR that you are restoring reflects, within the Partition Table, the exact geometry of the disk. It is extremely important that when you make an image of your System partition AND the MBR that you make a physical note on paper (not on your PC) that tells you exactly the information contained within the Partition Table of that MBR.

 

Great. Thanks again for your help.

 

Great info!

What if you recreate the same number of partitions, but slightly different sizes? Then you restore the System Image with an older version of TI, which does not allow you to select the MBR. Will the MBR that gets restored corrupt the existing MBR, and not allow it to boot?

I believe that's what happened to me here.

 

With Windows it is not always possible to predict with certainty exactly what will happen. However, it is quite possible - even probable - that Windows will fail to boot if the information in the Partition Table within the MBR is even slightly different to the actual physical geometry of the disk.

When you make changes to the disk geometry with any of the normal tools (e.g. Windows Disk Manager, Partition Magic, Acronis Disk Director...), as part of that process the MBR is rewritten (or more specifically the Partition Table information is rewritten because the Master Boot Code and Disk Signature remain as is).

Best practice dictates that everytime a change - no matter how small - is made to the disk partitions, that you create a new image of the MBR to reflect those changes.

For most users once the disk layout has been decided then it normally remains that way for a long time. In these cases it is quite practical to backup the MBR together with the entire disk or together with the system partition. However, if for some reason, you frequently make changes to your disk then it would probably be more convenient for you to backup your disk or system partition and EXCLUDE the MBR. You would then backup the MBR separately when you made disk changes.

 

Hi Tabvla,

Unlike we originally thought, it turns out that the Partition Table is not the reason for recreating the original number of partitions on a replacement drive. If not already done, please read the Acronis Support clarification in this previous thread titled <Reflections on Build 3567 and MBR>.

Regards

 

Hi Menorcaman

Hmmm... thanks for the link. Makes interesting reading. Perhaps Acronis Support is being a little "loose" with their use of the terminology - understandably as the subject is complex and probably totally irrevelant to 99% of users.

However, in the interests of clarity......

Under Windows the Boot Partition and the System Partition are not necessarily the same thing. Again, in 99% of cases they will probably be the same partition but this is purely coincidental rather that a requirement.

The system partition refers to the disk volume that contains the hardware-specific files that are needed to start Windows namely - Ntldr, boot.ini, and Ntdetect.com. These 3 files together form the XP boot loader. (Things will change with the release of Vista, where Microsoft have at last developed a proper boot manager).

The boot partition refers to the disk volume that contains the operating system files, which in the case of Windows will be identified as WINDOWS\..

In a Windows-based system there can be only one system partition and this must reside on the first disk which is designated as Disk_0. There can be any number of boot partitions and they can reside on any internal disk (Can be an external disk but you need to be very techy-savvy to set it up).

Yes, the terminology is confusing but sometimes the guys in Redmond put something extra in the coffee I think

Does that clarify or confuse the issue

 

Hi again Tabvla,

I guess that depends on whether one understood what the issue was in the first place .

Regards

 

As this relates to restoring images to larger drives, after I've restored the partitions where I want them (including resizing), the last step would be to restore the MBR and Track 0 from the image of the smaller drive? Will this work?

 

It should.

 

It did.

 

Good.

 

Hello Everyone,
I am having MBR error and or hal.dll corrupt/missing problems when trying to restore from a fully functioning Seagate to a new larger Western Dig, as described over on the "hal.dll missing AGAIN" thread. You guys seem very knowlegable on the MBR subject, and any thoughts you might have on my inability to restore due to either "missing/corrupt hal.dll" or "MBR error- press a key" would be much appreciated. I don't mean to hijack this thread, but it appears the problem here has been solved, so I thought I would beg for help from some of you guys.
Thanks
Bill

 

Hi Bill,

I would suggest you start a new thread with your own topic header. Some will not read your post tagged to the bottom of this long thread.

Just a suggestion!

EDIT: I see you already have a thread started - the mods would suggest you post back to your initial thread for your solution. Give the more tech minded time, they will assist you the best they can!

Allen

 

Thanks Allen.