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Re: custom partitioning



On 7/29/07, Charles Curley <charlescurley charlescurley com> wrote:
> On Sun, Jul 29, 2007 at 12:37:21PM -0800, Kam Leo wrote:
> > On 7/29/07, Charles Curley <charlescurley charlescurley com> wrote:
> > > 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.
> > >
> > > --
> > >
> > > Charles Curley                  /"\    ASCII Ribbon Campaign
> >
> > Charles, the information seems to conflict with that provided by Microsoft:
> >
> > [ref. http://support.microsoft.com/kb/323967/en-us]
> >  Any drive on a Windows-based computer can have a maximum of four
> > partitions, which can be made up of up to four primary partitions or
> > which can be made up of up to three primary partitions and one
> > extended partition. You can divide an extended partition into a number
> > of logical drives, which extends the four-partition limit.
>
> Hi, Kam.
>
> This article refers to several variants of Windows 2000. I was careful
> to restrict my remarks to Mess-DOS.
>
>
> >
> > [ref. http://support.microsoft.com/kb/41189/en-us]
> > The maximum number of logical drives that can be contained in an
> > extended partition is 23. Thus, with an active MS-DOS partition, and
> > all 23 logical drives (in the extended partition) allocated, this
> > gives 24 hard-disk drives (23 + 1) that can be used, in conjunction
> > with other virtual RAM drives, network drives, and floppy-disk drives.
> > The maximum number of total drives that MS-DOS can use is 26: Drive A
> > through Drive Z.
>
> Either the first statement is flat out wrong (not impossible) or else
> MS fdisk has had a bug in at least two versions (also not
> impossible). I distinctly recall experimenting in Mess-DOS 3.3 and
> again in 6.22 and finding a limit of four logical partitions per
> extended partition with fdisk. (3 extended * 4 logical) + 1 primary =
> 13.

FWIW: I also found the same information in the MS-DOS 5.0 User's Guide.

> Also, this article refers to "_an_ active MS-DOS partition, and all 23
> logical drives (in _the_ extended partition)" (emphasis added), as
> though the only way one could do it was one primary and one extended
> partition. This is incorrect.

The quote is from an article regarding the maximum number of logical
drives. On a single bootable DOS drive there must be at lease one
primary partition and a maximum of one extended partition. More to the
point is that there is a limit to the number of drives one can have.
Anyone needing to use a DOS based bootdisk is forewarned.

> The statement about drive letters is irrelevant to the subject at
> hand.
>
> In any case, all of this is moot given the restriction of libata.

The max SCSI drive limit doesn't effect me but it sure will effect the
guy at my LUG who crams his multi-boot system (over 16 distros) with
the flavor of the month.

> >
> > Where did you obtain yours?
>
> Experimentation.
>
> --
>
> Charles Curley                  /"\    ASCII Ribbon Campaign
>


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