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An Introduction to Full Virtualization With Xen (Linux.com)

An Introduction to Full Virtualization With Xen (Linux.com)

Posted Oct 23, 2012 23:55 UTC (Tue) by Lennie (guest, #49641)
In reply to: An Introduction to Full Virtualization With Xen (Linux.com) by cyanit
Parent article: An Introduction to Full Virtualization With Xen (Linux.com)

Xen has certain features KVM does not, I'm not well versed in these things. But I think this is at least one:

http://wiki.xen.org/wiki/Remus like VMWare which allows state of a VM to be replicated over a highspeed link to an other machine for failover.

And I keep reading Xen is faster than KVM, but I haven't tested that in my environment yet.


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An Introduction to Full Virtualization With Xen (Linux.com)

Posted Oct 24, 2012 8:44 UTC (Wed) by robert_s (subscriber, #42402) [Link]

"And I keep reading Xen is faster than KVM, but I haven't tested that in my environment yet."

From what I've seen, Xen is faster than KVM about half the time, and vice versa the other half.

And it's hard to predict which will be faster for a particular workload.

An Introduction to Full Virtualization With Xen (Linux.com)

Posted Oct 24, 2012 9:59 UTC (Wed) by Lennie (guest, #49641) [Link]

I know Phoronix might not be all that populair with the development community, but their results showed something like that too.

Judging by some of the other things I've seen online, KVM has gotten better and Xen and KVM seem to be getting closer in performance and I think I've even seen them supporting paravirtualisation APIs from each other.

An Introduction to Full Virtualization With Xen (Linux.com)

Posted Oct 24, 2012 13:20 UTC (Wed) by cas (subscriber, #52554) [Link]

Remus sounds useful.

For KVM, there's plain old migration.

It's not the same as VM mirroring, but if you don't have the hardware (or the need) for completely transparent VM failover, you can do something similar with virsh save and virsh restore of a currently running VM.

The VM is paused for as long as it takes to save, transfer to another machine, and restore the VM's state.

Works well enough with shared storage (like NFS), and (i haven't tried this) might even work if you save to stdout, pipe over ssh, and then restore from stdin.

Otherwise if the VM or the server it's running on has died, DRBD or iscsi volumes or even qcow2 on NFS can be used to boot a VM on another server.

An Introduction to Full Virtualization With Xen (Linux.com)

Posted Oct 24, 2012 13:50 UTC (Wed) by Lennie (guest, #49641) [Link]

Most people don't need something like Remus.

If you want some form of failover it is usually better to have 2 VM's in proper failover configuration. In a way that fits the software involved.

But the question was why Xen, so I thought I'd mention it. :-)

An Introduction to Full Virtualization With Xen (Linux.com)

Posted Oct 24, 2012 15:45 UTC (Wed) by Lennie (guest, #49641) [Link]

Maybe I should add that Remus does not work well over a WAN-link (you need lowlatency). So you probably can't use it for failover to a different datacenter either.


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