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Re: linux software RAID with hot-swap hardware

On Sat, 25 Jan 2003 14:15, Fraser Campbell wrote:
> > > the way I've tested it also works with
> > >
> > > install-mbr /dev/md1
> >
> > Why would you want to use install-mbr on a RAID device?
> >
> > I use install-mbr for the MBR on the hard drive (/dev/sda and /dev/sdb in
> > this case) and then have it load the real boot block from /dev/md1 which
> > was created by LILO.
> In my experience a lilo.conf such as this works:
>     boot=/dev/md1
> Simply run lilo thereafter, you will see that it automatically installs
> boot sectors in both drives.  Like this:
>     boot = /dev/hda, map = /boot/map.0301
>     Added Linux *
>     boot = /dev/hdc, map = /boot/map.1601
>     Added Linux *

That looks like an old version of LILO.  The latest LILO in Debian is 22.3.3 
and doesn't work like that.

> The above is from a Redhat 7.3 system but this worked back in Redhat 6.2, I
> have also done this with a sid system within the past month.

Strange, it doesn't work like that for me on my SID systems, and I haven't 
made a new release of LILO since September last year.

> In the above case /dev/md1 is a 24MB partition mounted as /boot, consisting
> of /dev/hda1 and /dev/hdb1.  Since lilo is supposed to get past the 1024
> cylinder limit these days that is probably not relevant.

Correct, and on modern LBA drives 1024 cylinders should be large enough for 
the entire root file system anyway.

> In testing I was able to boot with hda only (that one's obvious), I was
> able to boot with hdc only (both directly using BIOS and using lilo
> installed on floppy).

You've got a good BIOS then.  The only time I've had that work for me was when 
using SCSI on a machine with hot-swap drives (it cost enough so you expect 
such things to work).  For desktop machines I buy mostly what's cheapest.

> I'm 90% sure that I physically moved hdc so that it became hda and was able
> to boot perfectly but it was getting late and I lost track of what I was
> testing.

That used to tend to not work on the older versions of LILO with a default 
setup.  With the re-write of the boot code the default seems to work well for 
that (but may have problems with the drive as /dev/hdc).

> All partition types are set to RAID Autodetect (FD), I believe that may be
> important.

Of course.  The root file system on RAID won't work unless you have the 
partitions labeled as 0xfd or have an initrd that's programmed for it.

This is an interesting discussion, but you didn't answer my question of why 
anyone would want to run install-mbr on a RAID device.

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