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Date:      Thu, 23 May 2002 12:30:40 +0930
From:      Greg 'groggy' Lehey <grog@FreeBSD.org>
To:        Siegfried P Pietralla <siegfried.pietralla@eds.com>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: opinion on possible vinum config
Message-ID:  <20020523123040.X45715@wantadilla.lemis.com>
In-Reply-To: <16649A8D5C73D51183B80008C728EEB7CC0A8F@AUSYM103>
References:  <16649A8D5C73D51183B80008C728EEB7CC0A8F@AUSYM103>

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On Thursday, 23 May 2002 at 10:59:34 +1000, Pietralla, Siegfried P wrote:
> hi all,
>
> i've just stumbled across vinum and growfs and i'd like an opinion on the
> feasibility of the following implementation:
>
> set up a new disk as one all encompassing partition to be used as one vinum
> drive. then create a vinum volume for each required mount point and create
> one plex per volume. then add subdisks in 100Mb increments to each plex as
> required and use growfs to extend the fs each time a subdisk is added.
>
> does anyone see any major drawbacks?

This is pretty much the way it's intended to work.  Of course, you
don't have any added reliability with only one plex, but I assume
you're taking this into account.

> i realise that any fs activity that spans a subdisk boundary will
> involve an extra seek, but at one per 100Mb i don't have any
> problems with that. my aim here is merely to implement a flexible,
> controllable filestore layout - performance as such is not an
> issue. i notice that there are limits in vinum: 256 volumes/system (
> not an issue ) and 256 subdisks/plex ( limiting me to 25.6Gb / mount
> point in my scenario - i can live with that ). it does not mention a
> subdisk/drive limit e.g. a 60Gb drive would have 600 x 100Mb
> subdisks - is this a problem?

There's no hard limit for the number of subdisks on a drive.  At some
point you'd run out of space for configuration information on the
disk.  This would probably occur at round 1000 objects in the total
Vinum configuration.  If this becomes an issue, I'll have to implement
a different way to store the config information.

> also, is there a limit on how many times you can growfs a fs?

Hmm.  There could be.  I'd have to look at how it works.  There are
some issues like the size of a cylinder group which might be a
problem.  Maybe the authors will reply.

Greg
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