Re: [Xen-users] why LVM? why not Extended Partitions?

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> My problem seems to be related to the fact that my setup is a "home-setup",
> where I replace my VMWare Workstation with Xen. The problem occurs when you
> want to use your DomU sometimes as bare-metal and sometimes as a DomU, and
> if your domU kernel does not have necessary LVM modules and tools.

Ah OK.

We usually recommend LVM in dom0 for managing domU storage.  I generally 
suggest that if people are doing that they don't want to run LVM in the domU, 
because then you have two levels of LVM and it makes things confusing to work 
with.

If you want to have a guest that's either a domU or a bare-metal OS then I 
agree that using normal partitions is better.  This is what we used to do 
when testing out Xen guests and it worked fairly well at the time.  I'd 
recommend that you abandon using LVM for your purposes (at least for the time 
being) in order to make things easier for yourself whilst you sort out 
whatever other problems you come up with.

If you're not wanting to do stuff like resizing volumes, it doesn't really 
matter what you're using anyhow.

Cheers,
Mark

> 1) As domU bare-metal kernel can't see LVM volumes, I'm locked up at boot
> on bare-metal.
> 2) Even though DomU kernel has LVM, when you try to run it on bare-metal,
> you can't use LVM as a whole disk image, you can just use it like a
> partition. A disk image with partitions, inside a LVM volume, can't be
> easily mounted if I'm not wrong.
>
> Another point maybe related to my setup, is that my LVM volume group is
> fully utilized and when I need to resize or shrink, I'm having a lot of
> trouble. I guess I need to read more about LVM.
>
> Thanks a lot for the responses.
>
> Br,
>
> Emre
>
> On Nov 26, 2007 4:38 PM, Tomasz Chmielewski <mangoo@xxxxxxxx> wrote:
> > Emre Erenoglu schrieb:
> > > Hi,
> > >
> > > This is for HVM guests.
> > >
> > > I'm using LVM at my home setup for my DomUs, but having some issues
> > > with "mounting, umounting" the partitions inside the DomUs, as they are
> > > actually a disk image. Some of the kernels of my DomU's don't have LVM
> > > support at all, making it another issue.
> > >
> > > Why don't we just use Extended Partitions? What is the added benefit of
> > > LVM to us? I read around that it also includes a little overhead. When
> > > it comes to extension, shringking, modification etc, extended
> > > partitions are just as good, as you can use many proved commercial
> > > products to resize your partitions easily.
> > >
> > > Am I missing something here?
> >
> > Yes, in several points.
> >
> > 1. It's dom0 which needs LVM support; domUs don't need it. In fact,
> > whatever you use on dom0 as a storage for domU (LVM, disk, partition,
> > file etc.) doesn't matter from the domU point of view - in the end, domU
> > sees "a disk" anyway.
> >
> > 2. How many partitions can you have with extended partitions? I think
> > it's 16 maximum. I also think there is a maximum size (1 or 8 TB, I
> > don't remember) old-style partitioning can handle.
> > But I guess it won't matter for smaller setups anyway.
> >
> > Let's consider you have 3 partitions with different size, and some free
> > space after them:
> >
> > [ A     ][ B   ][ C       ][ free     ]
> >
> > You find that partition B is too small, and you want to resize it? Super
> > easy with LVM, and lots of effort when using old-style partitions.
> >
> > Still LVM not fun for you? It has some additional goodies (like
> > snapshots, etc.).
> >
> >
> > --
> > Tomasz Chmielewski
> > http://wpkg.org



-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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