[CentOS] installing centOS on extended partition

Robert Heller heller at deepsoft.com
Thu Oct 14 14:45:44 EDT 2010


At Thu, 14 Oct 2010 13:57:58 -0400 CentOS mailing list <centos at centos.org> wrote:

> 
> Robert Heller wrote:
> > 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
> <snip>
> > 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
> <snip>
> Ah, but what about hardware raid, say, a Dell PERC 7, with the two
> internal drives raided by that, *not* by software? I'm not sure I can see
> them as separate disks to grub-install.

With hardware RAID, the BIOS, lilo/grub, Linux, etc. just 'see'
whatever logical disk(s) the hardware RAID controller presents to the
system. The underlying structure is 'hidden' from view by the hardware
RAID controller. With most (true) hardware RAID controllers, the
logical disks should up as SCSI disks (usually with some 'fake' drive
model number), by using the kernel's SCSI disk abstraction layer (the
DAC960 driver does its own thing as far as a block structured
abstraction). When you write to the MBR of this 'disk', the hardware
RAID would mirror (or whatever, depending on the level of RAID -- with
only 2 disks, it would be either RAID0 (striped) or RAID1 (mirrored))
the writes. I was only talking about Linux's *software* RAID, which does
NOT apply to MBRs (which cannot be part of software RAID sets, unless
whole raw disks are being RAIDed, in which case there isn't a MBR at
all, or not something the *BIOS* can deal with as such).

> 
>        mark
> 
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>      

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