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Re: [Fedora-xen] xen and lvm



Augusto Castelan Carlson wrote:
I'm using fedora 7 for both host and guests. I would like to be able
to borrow unused space from one guest to be used in another one.

Looking for how to do that I only found instructions from people that
creates logical volumes and install the system using debootstrap. I
would like to use virt-manager to install my guests with lvm. How can
I do the partitioning for guests during my host install?

I think a number of separate issues to address here.

The advantages of LVM when combined with virtualisation or Xen are that you can create guest partitions easily and flexibly, that they can have nice names, and that you can resize and also delete them simply. LVM also lets you do this flexibly across physical disks, add extra physical disks if you run out of space, and so on.

So the basic command you need is:

  lvcreate -L 10G -n myguest VolGroup00

which would create a 10 GB partition called /dev/VolGroup00/myguest within an existing volume group called VolGroup00. (This isn't going to be a tutorial about LVM - there are plenty out there, go and use Google).

With the partition created above, just use the name of the partition directly within the virt-manager creation dialog. Forthcoming versions of virt-manager will be able to do the provisioning of LVM storage more automatically. If you want to follow this work, take a look at libvir-list.

This doesn't address directly your problem "to be able to borrow unused space from one guest to be used in another one". All that you'll get with basic LVM is the ability to resize one guest down and another guest up.

If all your guests are "related" -- that is they are derived from say a single distribution, there are several options: run an NFS server and share parts of the guests' filesystems, eg. home directories or /usr if you're feeling adventurous.

You could also look at LVM snapshotting, which will let guests "share" a single installation, but writes all modifications to their private partitions. The disadvantage of snapshotting is that although your guests start small, they grow indefinitely over time and later common changes cannot be shared.

Rich.

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