[CentOS] installing centOS on extended partition

Thu Oct 14 17:50:58 UTC 2010
Robert Heller <heller at deepsoft.com>

At Thu, 14 Oct 2010 09:53:52 -0700 CentOS mailing list <centos at centos.org> wrote:

>   On 10/14/10 6:53 AM, m.roth at 5-cent.us wrote:
> > Ritika Garg wrote:
> >> Can CentOS be installed on an extended partition? System has the following
> >> partitions:
> >> OEM(reserved)-78MB(primary)
> >> System-100MB(primary)
> >> C-55GB(primary)
> >> D-100GB(extended)
> >> Can I divide D into 2 parts:70GB and 30GB and install CentOS in the 70GB
> >> logical partition?
> > Of course. Extended or primary is an old, old DOS separation, but once
> > they exist, everything just treats it as another partition.
> >
> /boot still has to be on a primary, doesn't it?

No.  The *only* thing that needs to be in any partitular place is the
boot loader -- this is a BIOS thing: the BIOS wants the boot loader (or
actually the first stage of it) in the MBR of the first disk.  Both
Lilo and Grub can access any disk or partition that can be accessed by
the BIOS.  Lilo cares not about 'partitions' at all: it does raw disk
access using raw LBA32 (modern) or CHS (old) addressing).  Grub
understands ext2 file systems.  Neither Lilo nor Grub understand about
LVM or RAID (they don't actually need to).  /boot cannot be inside a
LVM VG.  It can be a *mirrored* (RAID1) set.  Trickyness: if your /boot
raid set is on the first & second disk (eg /dev/sda and /dev/sdb or
/dev/hda and /dev/hdb) and you want to be able to boot if the first
disk dies, make sure that the boot loader is on both disks (eg do a
grub-install on the second disk as well as the first disk, similar
magic for lilo).  That way if the first disk of the raid mirror set
dies, you can 'swap' the bad drive out, put the good *second* drive in
as what the BIOS sees as the first drive (if real SCSI or hot-swapable
SATA, merely removing the bad drive is enough -- for IDE one needs to
reach inside and have fun with cables and/or jumpers). You system will
boot (with a degraded RAID set).  (You can install a replacement drive,
partition it, add it to the raid set and have things rebuild).

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Robert Heller             -- 978-544-6933 / heller at deepsoft.com
Deepwoods Software        -- http://www.deepsoft.com/
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