Re: [Xen-users] Newbie Question on Comparisons/Advice

[Geert Janssens <info@xxxxxxxxxxxx>]

On Monday 28 April 2008, Michael Jinks wrote:
> On Mon, Apr 28, 2008 at 01:38:01PM -0300, Tim Cook wrote:
> > I have been looking at XEN the past few days and trying to digest all
> > the great documentation.  It seems to me that I would want Windows to
> > run in an LVM VBD environment???
>
> You could, but given the risks of shrinking a filesystem (I've done it
> successfully with ReiserFS, once, just to see if it worked; never tried
> with any filesystem that had seen serious use and never with ext[23])
> you might as well make a disk file within your existing filesystem.  If
> you've been reading Xen docs you've probably run across examples for how
> to do that.
>
I have shrunk an grown ext3 partitions on LVM just fine. I have never had any 
problems with this, although I won't imply this is without risk. You should 
always have a backup available before starting this operation !

> I've read (have not done comparisons for myself) that a loopback-mounted
> file in a Linux system will give comparable performance to a raw device
> (i.e. LVM volume).  The advantage of LVM is in the flexibility, but
> you're in a situation where the up-front costs (shrinking filesystem,
> spending some time with the LVM docs) might outweigh the advantages.
>
> > I've been using Linux at various levels since 1994.  BUT! I haven't kept
> > up with technical stuff lately and really have only a vague clue about
> > LVM.  When I installed Fedora I just accepted the defaults which created
> > just one logical volume.  Now after reading the XEN docs I think that
> > there will be a need to have two LV's?  Then reading the LVM docs it
> > seems that this will require reducing the filesystem (ext3) size before
> > reducing the LV size thus putting my data at risk.
>
> If you want to do it that way, yeah, you'll need to shrink the
> filesystem, then you'll need to shrink the (virtual) device it lives on,
> and then you can create a new virtual device in the freed space.  But
> it's quicker just to dd a bunch of zeroes into a file and treat that as
> a disk.
>
> > This now brings me back to having to start over reinstalling Fedora;
> > from my understanding.
>
If you can afford to reinstall the system, you can probably also afford the 
risk involved in resizing an LVM. The good news is, fedora comes with a nice 
GUI interface that can do the resizing of both the ext3 partition as the 
logical volume it is stored in. This tool is called system-config-lvm or you 
find it in the menu under Administration - Logical Volume Management (That's 
in the KDE menu's anyway, I'm not sure where it's put under Gnome). It's very 
easy to use and until now it has never failed me.

Hope that helps,

Geert
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