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Date:      Sat, 14 Jul 2001 11:13:41 +0100
From:      Mark Drayton <mark.drayton@izr.com>
To:        Greg Lehey <grog@FreeBSD.org>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: Vinum mirrored/striped confusion
Message-ID:  <20010714111341.B63502@drex.staff.izr.com>
In-Reply-To: <20010714092821.F99931@wantadilla.lemis.com>; from grog@FreeBSD.org on Sat, Jul 14, 2001 at 09:28:21AM %2B0930
References:  <20010714004038.A58799@drex.staff.izr.com> <20010714092821.F99931@wantadilla.lemis.com>

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Greg Lehey (grog@FreeBSD.org) wrote:
> On Saturday, 14 July 2001 at  0:40:39 +0100, Mark Drayton wrote:
> > 
> > I don't quite understand why mirroring two plexes containing the
> > same subdisks is beneficial. What happens if, say, disk 1 fails?
> 
> If you mean d1, then you'll lose the first 512 MB of plex 0 and the
> last 512 MB of plex 1.  These parts of the volume will no longer be
> mirrored.

Ah, I see now.

> > I imagine both plexes will be faulty and the volume will be down
> 
> This is incorrect.  The volume will remain up.

Excellent! I assumed a volume requires at least one 'up' plex to be up.
Obviously this isn't the case.

> > Aside from this possible difference, is one of these two setups
> > going to perform better (for a mail server) than the other?
> 
> Well, the second config only has half the storage :-)  But if you made
> those 1 GB subdisks, the performance should be comparable.

Okay. Which of these configurations do you recommend? As far as I know,
both configurations perform equally well, and a disk failure in either
case will result in half the volume not being mirrored but with the
volume remaining up. Is there any other pros/cons I should consider?

Thanks very much,

-- 

Mark Drayton
izR Company Ltd

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