[CentOS] Problem with dual-booting soft-RAID

Sat Jun 10 20:21:27 UTC 2006

On Sat, 2006-06-10 at 13:03 -0500, Johnny Hughes wrote:
> On Sat, 2006-06-10 at 19:31 +0200, Kai Schaetzl wrote:
> > Les Mikesell wrote on Fri, 09 Jun 2006 14:00:54 -0500:
> > 
> > > If you followed the HOWTO you may have accounted for the different drive 
> > > in the grub setup.
> > 
> > I don't know what you mean. I followed the howto and everything works. The 
> > point is: in my opinion it should *not* work. No matter which drive I 
> > remove it always boots successfully from the default 0 label, although that 
> > is on hd0 which is gone if I remove that drive. Theoretically, it should 
> > fail to boot from hd0 and fallback to hd1. This is IDE, not SCSI.
> > 
> > (I can also boot fine from hd1 if I interrupt the automatic boot, so grub 
> > is setup correctly.)
> > 
> > Kai
> > 
> 
> Kai,
> 
> One thing that I think you may be missing is this ...
> 
> In grub ... hd0 is the first found hard drive ... hd1 is the second
> found hard drive, etc.
> 
> IF ... you remove the primary hard drive (ie power it off, and unplug
> the cable) ... then the drive that is left (that used to be hd1) is now
> hd0
> 
> So ... when booting, it will be seen as hd0 and you won't have an hd1.
> 
> Well ... at least that is what I have experienced in the past ... maybe
> someone else who is smarter than me would care to comment / verify this
> behavior.

Further, in spite of my recent embarrassing confusion, *if* BIOS is
still involved (with RAID I don't know) and if you have "fail-over"
enabled in the BIOS (try C:, if that fails, D:,..., floppy, CD,...
etc.), the BIOS should change the device ID so that what was 0x81
becomes 0x80 (D: becomes C:).

Although that is in "Winspeak", the benefits to Linux accrue.

This presumes no earth-shattering changes in basic BIOS operations in
the last 6/7 years. We had EBDA then and Extended System Configuration,
so hopefully things are still similar.
> 
> Thanks,
> Johnny Hughes
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-- 
Bill
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