[ILUG] How much of MBR is partition table?

[Conor Daly]

On Fri, Feb 09, 2001 at 11:29:37PM +0000 or thereabouts, Pete wrote:
> Hi Conor,
> 
> The MBR contains Boot Code + Partition Table
> In my earlier (less educated) days I used the DOS Debug command to load
> and
> disassemble the bootup code.  One sector long and the first sector on
> the disk.
> 
> dd if=/dev/hda of=MBR.img bs=512 count=1
> 
> is the correct command ok,
> 
> but what exactly are you hoping to do?
> If you re-partition the drive, restoring the MBR afterwards is a bad
> idea.
> 

I'm planning to expand my ext2 real estate.  Using something like fdisk, the
original partition table can be restored if I screw up but I'm planning on
trying out parted.  However, *resizing* partitions with a dedicated tool
will move data around the disk so a partition table backup won't be any use.  

Yippee!  Imagine that, I'm about to convert another 2-3Gb from FAT32 to
ext2!

Which brings another question to mind.

I currently have ~12Gb FAT32 and ~6Gb ext2.  I've found it necessary to use
the FAT disk space for linux stuff (eg. MP3s) while I must use ext2 for
other stuff (eg. new mozilla build).  Now, I *could* make a file in the FAT
space and put an ext2 fs on that rather than repartition (I had to do this
at work to build mozilla) and therein lies the question.  What performance
hit is there in using an ext2 fs in a file on a FAT fs rather than using an
ext2 fs directly on the disk?  (AMD K6-2 350 MHz, 128Mb, standard EIDE
disks, RH7.0 stock kernel)  There is, of course, a hit in disk seek/thrash
since this bit of fs is physically seperated from the rest of the ext2
space.  Bear in mind that this is not running any mission critical stuff /
serving a big office with file, disk, shells etc and minor performance hit
may be preferable to a big partition / reinstall session.  Of course, such
an fs-in-a-file would be vulnerable to the kiddies pointing and clicking on
the "delete" button!

-- 
Conor Daly 
Met Eireann, Glasnevin Hill, Dublin 9, Ireland
Ph +353 1 8064217 Fax +353 1 8064275
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