I have Xen domU virtual machines running Windows. Each of them are installed in their own LVM logical volumes. I want to migrate them to another server with KVM on lvm to.
How can I do this faster and better with low downtime.
look at http://fedoraproject.org/wiki/Features/Xen_to_KVM_migration virt-v2v description: http://rwmj.wordpress.com/tag/virt-v2v/
A lot depends on how the LVM logical volumes are constructed and accessed.
If they are on a shared storage, it should just be a simple matter of creating new KVM machine configurations and pointing them towards the shared storage. You will need to ensure that the Xen configurations and KVM configurations match as closely as possible.
Then, you will need to shutdown the machines on the Xen and start them on the KVM. The Windows machines will probably complain that they have been moved and may need to be re-activated.
If they are not on a shared storage, then there is no easy way. You will need to replicate the LVM volumes. Since this will take an awful lot of time over the network, you may just want to re-create the machines on the new server.