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Date:      Tue, 2 Jan 2001 14:06:16 +0000
From:      Josef Karthauser <joe@tao.org.uk>
To:        Matraquilla@cs.com
Cc:        Roman Shterenzon <roman@harmonic.co.il>, Greg Lehey <grog@lemis.com>, freebsd-stable@FreeBSD.ORG
Subject:   Re: vinum malfunction!
Message-ID:  <20010102140616.B1391@tao.org.uk>
In-Reply-To: <d6.7493e7.278332c6@cs.com>; from Matraquilla@cs.com on Tue, Jan 02, 2001 at 08:33:58AM -0500
References:  <d6.7493e7.278332c6@cs.com>

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On Tue, Jan 02, 2001 at 08:33:58AM -0500, Matraquilla@cs.com wrote:
[cut]
> 
> As to your Vinum sacred cow, when are you going to accept that Vinum shall 
> (and could) never be more than an experimental beta that should never be 
> relied upon fully in a production environment.  If you want RAID, you get a 
> RAID controller.  If you like to play with explosives and are trying to get 
> away with cheap or free, by all means play with Vinum or its other software 
> siblings.
> 

I'm going to jump in here and defend Greg for a moment.

There is nothing wrong with doing RAID5 in software.  It allows a quick
fix without requiring the purchase of hardware for the cases where the
machine in question has plenty of spare CPU available (which is
most of them by todays standards).  It's cool.

On the other hand if it doesn't work then it's a nightmare!  (Like
having bad ram on your raid controller card :).

The problem with vinum RAID5 in -stable is that in my experience
there are some nasty bugs in it, and I don't believe that Greg has
managed to reproduce these himself and so is a bit confused as to
what is causing the trouble.

I'm worried that he may be inclined to believe that it is only a
small minority of people who are having problems with this.  I
would challange this view because I don't know _anyone_ who is
successfully using RAID5 under vinum.  They've all migrated away
to using dedicated hardware and thus solved their vinum problems
that way.

I don't know what it's going to take for Greg to get enough
information to fix the problem.  I spent a week trying to extract
a set of debug information for him that was useful enough that he
could work from it, but it seems that my week was just wasted
because it looks like I didn't capture the bug that he was expecting
:(.

I have tried to trust my home directory to vinum raid5 but failed. :(

To summarise.  The idea of software raid 5 is great, but it's got to
work otherwise it is dangerous.

I note that the BUGS section of the manual page doesn't exist.
There should be a warning to potential users that there are known
problems that can cause the data to become corrupted in some
configurations.

Joe


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