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Date:      Sat, 29 Nov 1997 17:25:26 +1030
From:      Greg Lehey <grog@lemis.com>
To:        David Dawes <dawes@rf900.physics.usyd.edu.au>
Cc:        hackers@FreeBSD.ORG
Subject:   Re: Drive Mirroring
Message-ID:  <19971129172526.39614@lemis.com>
In-Reply-To: <19971129165905.08819@rf900.physics.usyd.edu.au>; from David Dawes on Sat, Nov 29, 1997 at 04:59:05PM %2B1100
References:  <Pine.BSF.3.96.971128192019.1020A-100000@trojanhorse.ml.org> <199711290422.PAA23032@mother.sneaker.net.au> <19971129151057.57891@lemis.com> <19971129165905.08819@rf900.physics.usyd.edu.au>

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On Sat, Nov 29, 1997 at 04:59:05PM +1100, David Dawes wrote:
> On Sat, Nov 29, 1997 at 03:10:57PM +1030, Greg Lehey wrote:
>> On Sat, Nov 29, 1997 at 03:22:12PM +1100, Andrew Kenneth Milton wrote:
>>>> Would a software RAID implementation be able to cope with having a drive
>>>> removed?
>>>
>>> The last implementation I saw of software RAID on Solaris didn't
>>> (about two years ago).
>>>
>>> It wouldn't boot from the secondary drives,
>>
>> Booting is a different matter.  It's a lot more complicated, since you
>> need to explain RAID to the bootstrap.  I don't think that's
>> feasible.  But once the system is up and running, all other file
>> systems should be able to be RAID.
>
> The Veritas software that Sun supplies with their Sparc storage arrays
> these days does allow this.  It was one of the first things I tried
> (having a mirrored boot disk, removing the one it usually boots from,
> and booting from the other).  In the configuration I tested, the boot
> disk and its mirror were both "normal" disks attached to the primary
> scsi controller, and not disks in the storage arrays.  Mirroring is the
> only RAID type supported for boot disks though.

Yes, Tandem supplies Veritas as well, and Version 2 (which is even
more convoluted than Version 1) supports booting from a Veritas
volume.  It does this by imposing significant restrictions on the
format of root volumes.  It's not nice--I'd guess that it would make
more sense to have a really intelligent boot to handle things until
Veritas (or whatever) was up and running.

For the benefit of those who don't know Veritas: it runs as a number
of processes, notably the Volume Daemon.  Until that's up and running,
you can't mount Veritas volumes (virtual disks).

Greg



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