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Date:      Fri, 8 Nov 2002 11:32:29 +0100
From:      Bernd Walter <ticso@cicely8.cicely.de>
To:        Terry Lambert <tlambert2@mindspring.com>
Cc:        Lukas Ertl <l.ertl@univie.ac.at>, freebsd-hackers@FreeBSD.ORG
Subject:   Re: resizing mounted filesystems
Message-ID:  <20021108103228.GE46686@cicely8.cicely.de>
In-Reply-To: <3DCAE399.320D754@mindspring.com>
References:  <20021107154411.D210-100000@pcle2.cc.univie.ac.at> <3DCAE399.320D754@mindspring.com>

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On Thu, Nov 07, 2002 at 02:05:13PM -0800, Terry Lambert wrote:
> Lukas Ertl wrote:
> > how hard would it be to implement resizing of mounted filesystems?
> > Currently, growfs requires the filesystem to be unmounted, and this is
> > definitely a showstopper for FreeBSD when it comes to production use.
> > 
> > I'd really like to promote FreeBSD more in my organisation, where we
> > currently use mostly AIX, and I often hear (and have to say that it's
> > true) that the AIX LVM is so robust, stable and quite easy to use.
> > 
> > Could this feature be implemented once FreeBSD 5.0 is out with its
> > filesystem snapshot?
> 
> Nearly impossible, without a JFS.  You would need to be able to add
> new PP's to an LP, as you can do on AIX, or assign PP's to a "hog"
> partition, and them provide each LP with "hog limits", so that they
> can allocate PP's to themselves automatically, as needed, up to some
> high watermark.

It is doable - just not done.
E.g. Solstice Disksuite for Solaris does this.

> The problem is that the allocation space is spread over all cylinder
> groups, effectively as a hash.  This is the same reason it is
> recommended that you backup and restore to "defrag" when you run
> "growfs".

That's a performance reason.

-- 
B.Walter              COSMO-Project         http://www.cosmo-project.de
ticso@cicely.de         Usergroup           info@cosmo-project.de


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