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Re: Support for mirrored pair as root disk?



On Tuesday,  7 September 1999 at 10:09:19 +0100, Peter Galbavy wrote:
> On Tue, Sep 07, 1999 at 12:25:52PM +1000, Dale Shaw wrote:
>> Is there any way I can establish a mirrored pair of disks for the
>> operating system? A quick search of the archives doesn't turn up much
>> in the way of RAID controller support so I guess my only option is ccd
>> or RAIDframe?
>
>  ...
>
>> I asked Peter Galbavy early last month about using RAIDframe but I
>> don't think that's a happenin' thing just yet.
>
> It is on my mental list, along with cathing up with the small number
> of changes Greg Oster has made in the NetBSD code. I think that it
> should be easy enough to mirror the root disk, as long as the raidctl
> program is run before root is remounted. My main mental problem just
> now is how to make the initial mirror in a safe way.
>
> I am sure there is much more to it, and subtle gotchas, but as we have
> just started a four week contract for a client, time is even more
> scarce.

This is number one on the Vinum wishlist.  The problems I see are less
to do with setting up an initial mirror as that you can't boot from
it.  It would be impractical to have the bootstrap run vinum and keep
the *same instance* running after the kernel is started, so any
alternative would probably have to pull some fast ones.  I see about 3
possibilities:

1.  Boot from a standalone partition, the way System V does.  The
    standalone partition wouldn't be mirrored, but the only thing in
    there would be the kernel (maybe).

2.  Boot normally and then remount the root file system on a Vinum
    volume.  This would require going through all the vnodes and
    fixing them up.

3.  Put the root on MFS and swap to a Vinum partition.

I'd be interested if anybody had any comments on this.

Greg
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