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Re: Installation on RAID-only system

From: Jonathan Goldblatt
Subject: Re: Installation on RAID-only system
Date: Mon, 21 Mar 2005 07:09:13 -0500

>>>>> "Molle" == Molle Bestefich <address@hidden> writes:

    Molle> What am I doing wrong?

There are two types of access to a drive, physical and logical.
A non-raid system involves a physical access to get a disk block
and a logical access to interpret the block as a part of a
filesystem, e.g. filedata.

grub uses the BIOS provided by the manufacturer to get the
physical block and then uses its own code to handle decoding data
in the block to find files, etc.  

A raid system involves several physical accesses to different
disks (raw disk blocks) which is what gives the redundancy, a
logical access interpreting these different blocks as a single
logical disk block, and then a logical access to understand the
logical block as part of a filesystem.  Depending on the
implementation of the RAID there is either a BIOS provided by the
RAID manufacturer or OS software (that isn't available until
after booting the OS:-), to generate the checked logical disk

Even more confusingly, the RAID implementor usually tries to hide
the fact that there is a RAID present so that people just act the
same way whether there is a RAID or not, so say /dev/hde may mean
something entirely different depending on whether there is a RAID
installed or not, and /dev/hde may not even correspond to a BIOS
accessible partition that grub is willing to try to interpret)
grub can only work on a partition that is physically accessible
by the computer BIOS and that identifies itself as a partition
type that grub is knows it can interpret.

You can use the find command to discover this stuff.  I.e. 'find
/boot/grub/stage2' (or since I like having a separate boot
partition 'find /grub/stage2') from the boot command line
(immediately after rebooting, if you get my drift) will show the
partitions that grub can actually access.  You can use any file,
e.g. /config.sys (you are using DOS 3.3, aren't you?;-);
directories didn't seem to work the last time I did it.  To make
sure everything is hunky-dory you can try cat on the file to make
sure that grub can correctly read it.

Hope that helps,


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