Backup and Restore MBR

[Mike McCarty]

James Wilkinson wrote:
> Les wrote:
> 
>>   It has been decades since I looked at the disk structure.  I am
>>curious about the current "state of the art".  Can you recommend some
>>(heavy?) reading?
> 
> 
> That's odd -- the PC partition structure is a couple of decades old.
> You're probably up to date.

Well, the Microsoft MBR structure has been around since about 1982,
and was modified in about 1984 or so (for extended partitions
and more than four volumes per disc), and has since remained unchanged.

BUT there are other partition schemes around, like that used by
BSD. I'm not familiar with them enough to know when they came into
existence. It's worth knowing that other partitioning schemes do
exist, even on the PC.

> As far as I can see, http://en.wikipedia.org/wiki/Master_Boot_Record and
> http://en.wikipedia.org/wiki/GUID_Partition_Table are accurate. GPT is

Yes, I have looked there recently, and it looks completely accurate
to me, though I haven't read every line. This entry does distinguish
the several parts and kinds of PT as if they were separate structures,
while traditionally the MBR has been considered to have three parts:

code
PT
marker

with the PT having sub-structures contained within it. I would not
have worded the article that way, but what I saw (in five minutes)
looks correct. I haven't looked at the GUID entry.

> not yet used except on high end servers and Intel-based Apple Macs --
> since the existing PC partition structure has a hard disk size limit of
> 2 TB, this will have to change soon. (Yes, that also means it can't
> support RAID arrays with more usable space than 2 TB).

Would you explain this? I don't get why the PT structure imposes
a limit on the total storage used in the array. If the RAID
is done "below" the FS, but "above" the BIOS, I don't see how the PT
would prevent striping across discs to arbitrary sizes.

Mike
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