Backup and Restor MBR

[Kam Leo]

On 12/12/06, Mike McCarty <Mike.McCarty at sbcglobal.net> wrote:
> Aaron Konstam wrote:
> > On Mon, 2006-12-11 at 16:23 -0600, Mike McCarty wrote:
> >
>
>
> >>>>
> >>>>The MBR is the Master Boot Record, which is 512 bytes long
> >
> >
> > This is both true and not true. It is true that the whole 512 bytes is
> > called the MBR but if we mean what gnome-install updates as the MBR only
> > 446 bytes are in this MBR.
>
> The MBR has a structure to it. No question. The *code* portion (which
> is unimportant, actually, as it contains no useful information which
> cannot easily be gotten from other sources) is 446 bytes long.
>
> >>>>The MBR comprises three parts
> >>>>
> >>>>1. Code
> >>>>2. Partition Table
> >>>>3. Boot Record Marker (AA 55)
> >>>>
> >>>>No part of the MBR may be read or written without reading
> >>>>or writing all of it. Discs are, after all, BLOCK DEVICES
> >>>>which cannot transfer any amount less than a block (sector).
> >
> > It is true thast disks are block devices but are you saying:
> > dd if=/dev/hda of=/path/filename bs=446 count=1 will not put 446 bytes
> > into the file. And what does fdisk do when you do a write. What part of
> > the 512 byte block does it change.
>
> Yes, it puts 446 bytes into the file, but it puts 512 bytes
> on the disc.
>
> When fdisk writes the MBR, it writes 512 bytes. One cannot write
> less than one full sector to disc.
>
> [snip]
>
> >>>>Saving the MBR should be done in its entirety. Whether one wants
> >>>>to preserve the PT portion of the MBR when rewriting it on disc
> >>>>later is a decision to be made at that time. Not saving the original
> >>>>PT portion of the MBR is folly.
> >>>>
> >
> > Why exactly is it folly?
>
> If anything needs to be "saved" it is the PT portion of the MBR.
> The code portion is uninteresting and not particularly useful
> to save, since it can be gotten from a number of sources.
> The *important* information is contained in the PT. The stuff
> we can't get from another source easily.
>
> I'm not recommending only to save the PT portion. It's best
> to save it all. But if I had to choose between the code
> portion and the PT portion of the MBR, I'd save the PT part
> no question, and leave the code.
>
> >>When somebody states "No" four times in a row, and then gives incorrect
> >>data and actually bad advice, he needs to have his wrist slapped. I
> >>wasn't correcting *words*. I was correcting bad information and bad
> >>advice.
> >>
> >>Recommending not saving the entire MBR is BAD ADVICE, which he
> >>based on INCORRECT INFORMATION.
> >
> > What incorrect information is it based on?
>
> See right here below
>
> >>Advising someone not to back up the entire MBR, based on the
> >>misinformation that the PT is not part of it, is foolish.
>
> Mike
> --

Guys, please put a stop to this pissing contest.

In all of this you both left out that the OP needs a store that data
on media that is accessible for restoration.  That means not on the
drive where the MBR is to be restored!  Also, whatever boot
disk/device the OP uses needs to have the necessary device driver to
access the saved MBR data.