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

To: Emre Erenoglu <erenoglu@xxxxxxxxx>
Subject: Re: [Xen-users] why LVM? why not Extended Partitions?
From: Tomasz Chmielewski <mangoo@xxxxxxxx>
Date: Mon, 26 Nov 2007 16:38:55 +0100
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Emre Erenoglu schrieb:

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

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