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List:       linux-raid
Subject:    Re: Set up RAID over linux
From:       Edward Welbon <welbon () bga ! com>
Date:       1997-05-28 1:10:12
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I missed this message.  Delete if not relevent.

In a sense, I boot from a software raid.  My runtime root filesystem
resides on a soft raid (/dev/md*).  I have a cheesy little scsi disk that
is my start up boot device.  I have compiled into the kernel the initrd
support which lets me read in a filesystem from the start up disk to the
ram disk.  Once loaded the ram disk file system has a script /linuxrc that
is executed during boot.  The script contains an mdadd that enables the
runtime root file system on the soft raid.  The script writes the device
major+minor number of the md root filed system to the /proc file
"real-root-dev" (in my case/dev/md0 is major 9, minor zero so the correct
value is 0x900). 

/bin/echo 0x900>/proc/sys/kernel/real-root-dev

After unmounting /proc, /linuxrc exits with /dev/md0 ready to go and
the boot proceeds.  I end up with all my filesystems being /dev/md0
(excepting the small scsi disk).  Not the same as the adaptec controller
strategy (such as it is) but it works very nicely.  It is conceptually
similar to booting from a floppy.  It would work on the adaptec three
channel controller.

A pity that the adaptec 3 channel controller in not provided in an ultra
wide format. 

On Tue, 13 May 1997, Doug Ledford wrote:

> On Fri, 9 May 1997, Brian N. Borg wrote:
> 
> > Then, how is it that you can boot from a configured RAID on the
> > Adaptec?  It seems to me that all "software" is logic.  If the 
> > logic is there when the device is turned on, it can be considered 
> > "hardware" for all practical purposes.  You would still need to
> > boot dos to configure the arrays.
> 
> As I said, the magic very well could be in their sequencer code, which
> actually runs on the card.  However, under linux we can't use their
> sequencer code.

Ed Welbon; welbon@bga.com;
<a href="http://www.bga.com/~welbon/arachnid.html">the arachnid mail list</a>

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