Not sure if you saw the announcement on /. the other day. This project has some significant implications for LTSP.
http://www.cl.cam.ac.uk/Research/SRG/netos/xen/index.html
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Xen is a virtual machine monitor for x86 that supports execution of multiple guest operating systems with unprecedented levels of performance and resource isolation. Xen is Open Source software, released under the terms of the GNU General Public License. We have a fully functional ports of Linux 2.4 and 2.6 running over Xen, and regularly use it for running demanding applications like MySQL, Apache and PostgreSQL. Any Linux distribution (RedHat, SuSE, Debian, Mandrake) should run unmodified over the ported OS.
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They claim performance very similar to the native mode and far better than VMware.
Some of the more interesting features I have been playing with are a save and restore feature to snapshot the current state of a machine and migrate the live running machine from one computer to another.
There is also the ability to manage memory of the running virtual machines.
Imagine a farm of LTSP servers where the various application sets are run in separate VMs and can be pushed around the server farm without the users being aware.
It is not difficult to set up, although I haven't got everything working just yet.
4.2 Domain Save and Restore
The administrator of a Xen system may suspend a virtual machine's current state into a disk file in domain 0, allowing it to be resumed at a later time.
The ttylinux domain described earlier can be suspended to disk using the command:
# xm save ttylinux ttylinux.xen
This will stop the domain named `ttylinux' and save its current state into a file called ttylinux.xen.
To resume execution of this domain, use the xm restore command:
# xm restore ttylinux.xen
This will restore the state of the domain and restart it. The domain will carry on as before and the console may be reconnected using the xm console command, as above.
4.3 Live Migration
Live migration is used to transfer a domain between physical hosts whilst that domain continues to perform its usual activities -- from the user's perspective, the migration should be imperceptible.
To perform a live migration, both hosts must be running Xen / xend and the destination host must have sufficient resources (e.g. memory capacity) to accommodate the domain after the move. Furthermore we currently require both source and destination machines to be on the same L2 subnet.
Currently, there is no support for providing automatic remote access to filesystems stored on local disk when a domain is migrated. Administrators should choose an appropriate storage solution (i.e. SAN, NAS, etc.) to ensure that domain filesystems are also available on their destination node. GNBD is a good method for exporting a volume from one machine to another. iSCSI can do a similar job, but is more complex to set up.
When a domain migrates, it's MAC and IP address move with it, thus it is only possible to migrate VMs within the same layer-2 network and IP subnet. If the destination node is on a different subnet, the administrator would need to manually configure a suitable etherip or IP tunnel in the domain 0 of the remote node.
A domain may be migrated using the xm migrate command. To live migrate a domain to another machine, we would use the command:
# xm migrate --live mydomain destination.ournetwork.com
Without the -live flag, xend simply stops the domain and copies the memory image over to the new node and restarts it. Since domains can have large allocations this can be quite time consuming, even on a Gigabit network. With the -live flag xend attempts to keep the domain running while the migration is in progress, resulting in typical `downtimes' of just 60-300ms.
For now it will be necessary to reconnect to the domain's console on the new machine using the xm console command. If a migrated domain has any open network connections then they will be preserved, so SSH connections do not have this limitation.
Regards Darryl Bond
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