custom partitioning

[Charles Curley]

On Sun, Jul 29, 2007 at 10:43:50AM -0400, Michael Klinosky wrote:
> I just got another computer, and I'm stalled in the partitioning 
> department. I decided to forgo LVM, so I have some questions.
> 
> Does it matter in which order I create the partitions? Like, should I 
> create /boot first?

Some BIOSes cannot access beyond a given number of cylinders on a hard
drive. Thus the files to be loaded by the BIOS should be contained
entirely within the range up to that number. If you create /boot
first, you will keep those BIOSes happy, and will not cause any
problems for BIOSes that do not have that restriction.

> 
> On the 'Add partition' window is a checkbox: 'Force to be a primary 
> partition'. What's this? (It's not mentioned in the Installation docs.) 
> Do any partitions need it?

This has to do with the history of disk partitioning; it is a kludge
and a bad hack. Even the terminology is atrocious.

In short, there are four places in the partition table
of the master boot record (the first sector of the hard drive). These
are primary partitions.

To add more partitions, primary partitions can be relabeled as extended
partitions, which contain logical partitions. Under Mess-DOS, a given
extended partition can have no more than four logical partitions. I
don't know if any other OSs have this restriction. The logical
partition table for each extended partition is contained in the first
sector of the extended partition. You do not put file systems on
extended partitions; they are containers for primary and logical
partitions.

Thus to add up to four logical partitions, you must sacrifice a
primary partition. But you must have a primary partition to keep older
BIOSes happy (and perhaps current ones; I don't follow BIOS
development closely these days). So you can have up to 13 partitions
in a Mess-DOS compliant hard drive.

In any case, Linux' libata driver cannot recognize more than 15
primary and logical partitions, so that sets an upper limit.

So the only partition you should force to be a primary is /boot, which
should then become /dev/sda1. Let the disk partitioner allocate the
rest between logical and primary.

The article at http://en.wikipedia.org/wiki/Primary_partition is
pretty good, although it confuses things by conflating primary and
logical partitions.

-- 

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