On Sep 29, 2006, at 4:51 PM, Tracy R Reed wrote:
Not sure how VMWare and VMotion do it but when you migrate a Xen domain from one machine to another the Xen hypervisors on each machine communicate over the network and begin copying pages of memory from one machine to another without stopping the domain being moved. It keeps track of which pages were dirtied/changed during the copy and re-copies those. It keeps re-copying until it is no longer getting ahead and then it freezes the source domain, copies remaining pages and machine state (cpu registers, etc), then starts the copied domain on the destination machine. The freeze part usually only takes a few milliseconds so nobody notices. You can then rip the cables out of the old machine.
This is exactly how VMotion works as well. It generally uses a separate gigabit network between the nodes.
Are you saying that with VMWare and VMotion you can rip the cables out of a machine and THEN it seamlessly moves to another machine? I'd like to know how they do that.
No, to get a seamless move you have to put the node in question into maintenance mode, at which point it will do the VMotion (as described above) of hosts to other nodes with spare capacity, and then you can rip out cables.
If you just go ripping out cables, you'll fall back to VMware's HA functionality which will *notice* that the cables have been ripped and then bring any dead virtual machines back up on other hardware, but the state obviously isn't preserved since it just evaporated from the RAM of the machine with no cables. :)
-- Joshua Penix http://www.binarytribe.com Binary Tribe Linux Integration Services & Network Consulting -- [email protected] http://www.kernel-panic.org/cgi-bin/mailman/listinfo/kplug-list
