Fdisk: Linux logical on MSDOS extended ???

Fdisk: Linux logical on MSDOS extended ???

Post by paul coluc » Sat, 03 Feb 1996 04:00:00

   Is it possible to use Linux Fdisk to create a logical partition
on a MSDOS extended partition?

   The reason I need to do this is because my 1.08 GB WD 21000
drive has a primary (bootable) partition with Windoze 95/DOS 7.0.
This primary partition is 256 MB (4k clusters) and everything is
installed and running fine so I do not want to alter this partition.
I would like to have another 256MB dos partition for win 95, and
the remaining .5 GB dedicated to Linux.  MSDOS Fdisk won't allow
me to make another primary (msdos) partition.   I could make an
256MB extended partition and make all of it a logical DOS partition.
For the rest of the disk, dedicated to Linux, I would be restricted
to only 2 more primary partitions, and I would like more to keep my
filesystems on seperate partitions.

   What I could try is create an extended partition (> 256 MB) with msdos
fdisk.  Then I could create a logical dos partition of 256 MB on this
partition.  The rest of this partition would be made as Linux
logical partitions using Linux Fdisk.  I would also be able to create
2 addition Linux primary partitions on the rest of the drive (using
Linux Fdisk).  This would allow me to have 2 MSDOS partitions and
more than 2 (3,4,5,..) Linux native partitions.  Of course, this
plan of action relies upon the fact that I can create a Linux logical
partition with Linux Fdisk on a DOS extended partition (or could
try vice versa).  In other words, I require an extended partition
that has both Linux and MSDOS partitions.

    If this could be done, would there be a penalty of using a Linux
Fdisk logical partition on a DOS Fdisk made extended partition?
(performance, reliability, etc...).  Also, is there any performance
hit of using extended/logical over a primary (I don't think so).

I hae searched the HOWTO's on this idea of using Linux FDISK to
create a Linux logical partition on an extended partition created
by MSDOS Fdisk, but I have not found much.  The closest thing
I have come across was in the Installation HOWTO:

   "Note that MS-DOS FDISK will give you an option to create
    a ``logical DOS drive''. A logical DOS drive is just a logical
    partition on your hard drive. You can install Linux on a logical
    partition, but you don't want to create that logical partition
    with MS-DOS fdisk. So, if you're currently using a logical
    DOS drive, and want to install Linux in its place, you should
    delete the logical drive with MS-DOS FDISK, and (later)
    create a logical partition for Linux in its place."

In this example, the author suggests that the new Linux partition
could indeed be put on an extended partition created by DOS Fdisk.
I would like to know if this is adviseable.  Note I am not referring
to creating a *logical* Linux partition using MSDOS Fdisk as it
is clear this is not to be done.  I will ultimately be creating the
Linux logical partition with Linux Fdisk; I just want to put it on an
extended partition that was created using DOS Fdisk.

I appreciate any responses,
Paul Colucci
Computational Fluid Dynamics Laboratory
Dept. Mechanical and Aerospace Engineering
State University of New York at Buffalo


1. FDISK:: Extended partition VS Logical question

   I've built lots of linux images but I have problems when
putting on
allot of partitions > 5-8 partitions.  If I keep it to 4
then the and use fdisk then the load goes fine.  
   I'm confused over the man page description of fdisk.  It talks
1-4 being primaries and that logicals are numbered > 5.  If I
right I can't pick a p with fdisk and give it a 7 or pick an e
give it a 1.  
   So that's the background.  I can't matchup the numbering with
man page explination of extended.  How does a partition qualify
be extended which will be the "holding box" for logical
(I don't have a spare disk around to experiment with or I'd
this myself).  I guess if I have an 6 gig disk I'd make 1, 2, and
#3 partitions 1 gig and leave 3 gig for say 4 logical partitions.
What do I do with the 4 primary yet unspecified partition to make
it hold the logicals?  
   It seems this has been my problem with using disk druid.  When
I specifiy say 7 partitions and click OK on an install, disk
will return but my partition names and sizes will not be what I
Disk Druid did some arranging for me but sometimes it will take
some partition I want large /usr and put it to a size of 50 meg
which I had setup for /homes (in my setup 50 is plenty).  
   So what do I do with primarys to get an extended to hold
logicals corretly?
David Kirkpatrick

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