Re: [PLUG] Linux (Debian) and raid

["Aaron Mulder" <ammulder@alumni.princeton.edu>]

I think there's an interesting point here.  If you have 2 drives
/dev/hda and /dev/hdc in a software RAID 1 array, is there a way to
install Grub such that if /dev/hda dies then the machine can boot off
only /dev/hdc?  I would assume that "normally" Grub would only be
installed to /dev/hda and would look for an initrd in /dev/hda
somewhere, such that if /dev/hda failed then you wouldn't be able to
boot off /dev/hdc -- at least until you connect it to the other drive
cable, and/or until you reinstalled Grub.

Also, in the configurations that use separate (non-mirrored) swap
partitions on both drives, I would assume that the boot sequence would
bail if one of the swap partitions listed in /etc/fstab was not
present, and drop you into single-user mode.

Does someone have a procedure that will make it so that if you have
mirrored drives like in this example, and the first one dies or is
removed, you can just power up with the second drive only and *no*
changes and the OS will boot fully (though granted, probably griping
that the RAID set is broken)?  Or maybe that would never be possible
because maybe if the RAID set it broken it won't let you boot into a
regular read/write mode?

It does seem that using onboard RAID would avoid a lot of these issues
-- just with the caveat that you're protecting against hard drive
failure, not against motherboard/CPU/power supply/etc. failure.  (You
know, when 5 years later the interfaces for all of these have changed
and the local stores only carry the latest and greatest...)

Thanks,
     Aaron

On 5/26/07, Doug Crompton <doug@crompton.com> wrote:
> Now that this has been batted around a bit I have a few more questions.
>
> Using Raid 1, lets assume SW raid, and having the following partitiions -
>
> /boot, /root, /swap, /usr, /home, /lib, and maybe /opt (does Debian use
> /opt?) how would one setup raid?
>
> Does/should swap get included? Do all other partitions get included?
> Doesn't the system have to boot outside of raid before in recognizes a
> raid partition?
>
> What is confusing to me is that in my Intel MB driven raid the whole drive
> is part of the array. As far as the BIOS is concerned it is looking at one
> drive. In Linux, using SW raid, would not one drive have to boot linux and
> then the raid array is established? If this were the case then it is not
> truely raid because if that one drive failed it would not boot.
>
> I probably have this all wrong so if anyone can explain I would appreciate
> it?
>
> Doug
>
> ****************************
> *  Doug Crompton           *
> *  Richboro, PA 18954      *
> *  215-431-6307            *
> *                          *
> * doug@crompton.com        *
> * http://www.crompton.com  *
> ****************************
>
>
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