Partitions and MBR

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userX
Posts: 119
Joined: Thu Sep 15, 2011 11:51 am

Re: Partitions and MBR

Post by userX »

TeraByte Support(TP) wrote:
> userX wrote:
> > When I use IFL to backup a disk with only one partition, and if I select
> > the checkbox only for the partition to be backed up instead of the top
> > checkbox for the whole drive, am I correct in saying that the boot sector
> > of the partition would be backed up but the drive's MBR would not be backed
> > up? Thanks.
>
>
> The boot sector of a parttiion is always backed up, since it is part of the
> partition.
>
> When backing up an individual partition, the drive's first track (including the MBR)
> is always backed up with it, but it will not be restored when you restore that
> partition, unless you select the "Restore First Track" option on the
> restore options screen (see page 56 of the IFL manual).

Hi, Tom. If I seem to belabor this issue, you will have to excuse me; but I need to be real clear on some details because I recently hosed my system trying to restore selected partitions. When you said that "...the drive's first track..will be restored...", I need a little more clarity on this point. I may very well be wrong, but isn't it true that a drive's first track, which I understand as Track 0, includes the first sector of all the partitions on that drive, which would mean that I would be restoring information (i.e., Track 0) for other partitions in addition to that for an individual partition whenever I restore one partition only and include the option "Restore First Track"? Now, I understand that you said, in regard to the MBR, that only the code section but not the partition table would be restored, but doesn't the Track 0 contain partition information too for each partition existing at the time the backup was originally made? However, if any of these partitions have changed in size or position on the disk, would I not therefore have problems after the restoration of this old information?
Bob Coleman
Posts: 785
Joined: Fri Aug 12, 2011 5:58 pm

Re: Partitions and MBR

Post by Bob Coleman »

Why would you include the option "Restore First Track" when restoring only one partition?
TeraByte Support(TP)
Posts: 305
Joined: Wed Aug 31, 2011 4:22 pm

Re: Partitions and MBR

Post by TeraByte Support(TP) »

userX wrote:
> Hi, Tom. If I seem to belabor this issue, you will have to excuse me; but I need to
> be real clear on some details because I recently hosed my system trying to restore
> selected partitions. When you said that "...the drive's first track..will be
> restored...", I need a little more clarity on this point. I may very well be
> wrong, but isn't it true that a drive's first track, which I understand as Track 0,
> includes the first sector of all the partitions on that drive, which would mean that
> I would be restoring information (i.e., Track 0) for other partitions in addition to
> that for an individual partition whenever I restore one partition only and include
> the option "Restore First Track"? Now, I understand that you said, in
> regard to the MBR, that only the code section but not the partition table would be
> restored, but doesn't the Track 0 contain partition information too for each
> partition existing at the time the backup was originally made? However, if any of
> these partitions have changed in size or position on the disk, would I not therefore
> have problems after the restoration of this old information?

I think there's 2 key points here:
1. You normally don't need to use the "Restore First Track" option when restoring individual partitions. That is the exception, not the rule.
2. Even if you do use that option, the partition table will remain valid, no matter what.

But the first track does not include any first sectors from any partitions. For each partition, the first sector is, by definition, part of the partition itself, just like the last sector is. It is not part of the first track - it's part of the partition - and gets backed up and restored with the partition. The first track does contain the partition table in the first sector of the drive (the MBR sector). And, if you have an EMBR on the drive (i.e. you have BIBM or BING installed), they keep their own partiton table (MPT or Master Parttion Table) in the EMBR area, which immediately follows the MBR sector.

When you restore an individual partition (which includes when you restore an individual partiton from an image of an entire drive), there is normally no reason to use the "Restore First Track" option, which is why it is a non-default option. You should only use it if you have a known, specific reason to use it. But even if you do select "Restore First Track", as far as the partition table is concerned, it will simply update the existing MBR partition table (and the EMBR table if one exists) based on the partition(s) you are restoring - the same as it would do if you didn't select "Restore First Track". It will never restore a previous or invalid partition table to the drive, and it will never affect the first sector of any partition.

Again, the above applies to when you are restoring individual partitions. When you restore an image of an entire drive, it will always restore the drive exactly as it was, including the first track, partition table, and all partitions as they were on the source. There is no "Restore First Track" option in this case, because the first track is always restored, along with everything else that was on the source drive.
userX
Posts: 119
Joined: Thu Sep 15, 2011 11:51 am

Re: Partitions and MBR

Post by userX »

I need some clarification on another closely related point. I have another machine that I need to back up more regularly now as the activity on it will increase. It has two disks in it, and it currently has two operating systems, but that is likely to change because I will be adding one or two more. It also has Grub installed in the MBR. The second of the hard disks (sdb) has one of the OS (Linux) on it exclusively: that is, this OS is only (for now anyway) on this hard disk and this hard disk has only this OS on it. The other hard disk, sda, right now has only one OS (Windows) on it but it will be getting others (Linux) later on. The Windows OS is on the first partition and I do not expect to have much activity changing its size or contents.

In contrast, I do expect a lot of activity on the second hard disk (sdb), and I will need to back it up often. In addition, the whole disk is encrypted; so I should have to back up the whole thing each time while booted into the IFL CD environment. I would prefer not to have to backup both disks if I can avoid it. However, in this case my first and foremost concern is having a reliable restoration procedure, and efficiency becomes secondary.

Now then, Am I correct in saying that I should not have an issue with backing up and restoring of this second disk so long as I continue to backup the whole thing each time, REGARDLESS of what happens to the data or the partitions on the 1st disk in terms of changing content or size in between backups of the 2nd disk, even though they BOTH have and share one common MBR?

Under what circumstances would one want to make use of the option to Restore First Track?


These are the options I am using with my backup of the 2nd disk:


1. Is there any reason I should not use a Multiple File Set in the backup? I prefer this sort of procedure because it is easier to copy the files to a DVD medium as well, and if the process fails midstream, only one of the files in the set needs to be re-done.

2. Is there any point in my use of the option to Encrypt Data as the data on the disk is already encrypted, swap and all, and, as I stated earlier, the Grub program is installed in the MBR, which is clearly on the first sector of the other disk in the machine. On the other hand, is there "any" (unencrypted?) information of concern in terms of security measures contained on the first sector of this second disk, i.e., its volume boot record? If so, would this bit of information also get encrypted during a backup with IFL if I do in fact use the option to Encrypt Data? I ask this question also because it seems to me that, if I would choose to Encrypt Data unnecessarily during backup, all it would accomplish is add more time to the process without adding any value.

3. In addition, since the data is already encrypted and I am choosing to Validate Byte-for-Byte, is there any point in my choosing to use Compression? Correct me if I am wrong, but I am under the impression that compression would not have much effect on a drive whose data is already encrypted, and using it would, therefore, only add unnecessary time to the process without making much difference in the outcome spacewise. Nor am I sure whether either of the options for Enhanced Speed (A or B) would make much difference as compared with compression "None".
Bob Coleman
Posts: 785
Joined: Fri Aug 12, 2011 5:58 pm

Re: Partitions and MBR

Post by Bob Coleman »

Maybe slightly off topic, but note that if you create a single image file, you can use the free BingBurn to burn the file to DVD. BingBurn will break up the file as necessary to fit DVDs, I've had it happen that the burning of one disc fails and BingBurn simply asks for another one without affecting those already burned or to be burned.
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