Check out the following demo by Blip.tv account ‘VMware TV‘, expressing the difference between moving a VM from one physical server to another with downtime (Hyper-V Quick Migration) and VMware’s Vmotion, which offers zero downtime when transferring virtual machines.
Keith Ward over at Virtualization Review picked up the demo and writes about what happens in the video:
“The demo shows a Quick Migration of a Windows Server 2003 VM from one physical machine to another. At the same time, a Microsoft Dynamics client is trying to access a database residing on the VM. Through a constant ping of the VM, we can see how a) the connection to the VM is dropped for a time, and b) how the Dynamics client fails in its attempt to get the database information (an error box pops up, showing a TCP failure). Shortly thereafter, another popup informs us that the VM has actually been deleted. It’s re-started a few moments later.”
To be balanced, here’s what ‘Jeff’ recently posted on the Windows Virtualization Team blog:
After my last blog I received almost two dozen email telling me that VMotion was far superior for unplanned host downtime and that it was a much better HA solution because it could live migrate virtual machines. I’ve heard this fallacy espoused for many years and, folks, this simply isn’t the case.
In the case of unplanned downtime, VMotion can’t live migrate because there is no warning. Instead you must have VMware HA configured and the best it can do is restart the affected virtual machines on other nodes which is the same as what is provided with Windows Server 2008 Hyper-V and Failover Clustering.
Here are a couple of quotes from VMware’s own document, Automating High Availability (HA) Services with VMware HA.
Page 1 paragraph 2 states:
Using VMware HA, virtual machines are automatically restarted in the event of hardware failure…
Page 8 states:
How does VMware HA work?
VMware HA continuously monitors all ESX Server hosts in a cluster and detects failures. An agent placed on each host maintains a “heartbeat” with the other hosts in the cluster and loss of a heartbeat with the other hosts in the cluster and loss of a heartbeat initiates the process of restarting all affected virtual machines on other hosts.
HA monitors whether sufficient resources are available in the cluster at all times in order to be able to restart virtual machines on different physical host machines in the event of host failure.
The point being VMware HA and Hyper-V with failover clustering accomplish the same thing: virtual machines are RESTARTED on another node. No better, no worse. If you still don’t believe me, find one of your ESX Servers and go pull out the power plug. (Just don’t say I didn’t warn you.)
So what do you think about all this?
Well…I’d say that the VMware video is a clear demonstration of the differences between VMware’s VMotion technology and Microsoft’s Quick Migration technology.
I’d also say that it’s interesting that Micorsoft’s response deflects the issue and talks about VMware’s HA technology and – rightly – compares that the Hyper-V’s Quick Migration.
I don’t mind when rebuttals are accurate, which – if you read carefully – Microsoft’s is, but I do mind when you try to play a shell game and use redirection and slight of hand tricks to avoid addressing the issue at hand – which Microsoft did.
To be clear: VMware VMotion technology is NOT a DR solution. It is not advertised as being a DR solution. It is not intended to be a DR solution.
It is a solution for avoiding unnecessary downtime when you _know_in_advance_ that you need to take a host system off line. It is a solution for dynamically balancing workloads among a cluster of host systems (with the help of DRS – you can do it manually with just VMotion) without your service consumers having to have their service interrupted.
There are many users who, honestly, do not understand this and wrongly assume that VMotion is a DR solution. This is not a fault of VMware…they make it very clear what the role of each of these features is (from http://www.vmware.com/pdf/vi3_35/esx_3/r35/vi3_35_25_intro_vi.pdf):
VMware VMotion™ and VMware Storage VMotion – VMware VMotion enables the live migration of running virtual machines from one physical server to another with zero down time, continuous service availability, and complete transaction integrity. VMware Storage VMotion enables the migration of virtual machine files from one datastore to another without service interruption.
???? VMware High Availability (HA) – Feature that provides easy?to?use, cost?effective high availability for applications running in virtual machines. In the event of server failure, affected virtual machines are automatically restarted on other production servers that have spare capacity.
For the benefit of full disclosure – I am a user moderator for VMware’s community forums, and I do earn a living providing consulting services to customers who use VMware products. But I am also a strong believer in “doing what’s right” for my customers. I have, in the past, been both a Novell architect and a Microsoft AD architect.
I honestly hope that Microsoft is successful in delivering a top-quality, feature-rich virtualization platform. I also hope that Microsoft will refrain from trying to obscure the truth and “play fair” in the marketplace. Successful execution of both of these “hopes” would truly deliver “what’s right” for the customer.