Remus Project Brings Transparent High Availability To Xen

An anonymous reader writes "The Remus project has just been incorporated into the Xen hypervisor. Developed at the University of British Columbia, Remus provides a thin layer that continuously replicates a running virtual machine onto a second physical host. Remus requires no modifications to the OS or applications within the protected VM: on failure, Remus activates the replica on the second host, and the VM simply picks up where the original system died. Open TCP connections remain intact, and applications continue to run unaware of the failure. It's pretty fun to yank the plug out on your web server and see everything continue to tick along. This sort of HA has traditionally required either really expensive hardware, or very complex and invasive modifications to applications and OSes."

Comments

Already done by VMware

[Lurching]

They may have a patent too!!

Re:Himalaya

[teknopurge]

VM replication like this still has an IO bottleneck. This isn't magic: unless you move to infiniband you're not going to touch something like a Stratus or NonStop machine. By the time you add in the cost of the high-perf interconnects, you're on-par with the real-time boxes. All this convergence going on with people redesigning the mainframe but ass-backward with client/server gear. Makes little sense to me other than it being a gimmick.

By the time you get all the components that provide the processing and I/O throughput of those high-end boxes, the x86/64 commodity hardware cost advantage has evaporated.

Re:Wrong place to put a failsafe?

[dido]

This is something that the much simpler Linux-HA environment deals with by using something they call STONITH, which basically means to Shoot The Other Node In The Head. STONITH peripherals are devices that can completely shut down a server physically, e.g. a power strip that can be controlled via a serial port. If you wind up with a partitioned cluster, which they more colorfully call a 'split brain' condition, where each node thinks the other one is dead, each of them uses the STONITH device to make sure, if it is able. One of them will activate the STONITH device before the other, and the one which wins keeps on running, while the one that loses really kicks the bucket if it isn't fully dead. I imagine that Remus must have similar mechanisms to guard against split brain conditions as well. I've had several Linux-HA clusters go split brain on me, and I tell you it's never pretty. The best case is that they only both try to grab the same IP address and get an IP address conflict, in the worst case, they both try to mount and write to the same fiberchannel disk at the same time and bollix the file system. If a Remus-based cluster split brains, I can imagine that you'll get mayhem just as awful unless you have a STONITH-like system to prevent it from happening.