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Monthly Archives: April 2008

Reviving the Dormant Grand Architectures of IT with VMotion

Long-deferred vendor visions of agile data centers are finally coming true now that VMware virtualization with VMotion live migration has severed the ties that kept services fixed to x86 hardware.  Unfortunately, some vendors are trying to stage a revival with an inferior substitute for live migration.  Most notably, Microsoft is claiming that their "Quick Migration" feature is comparable to VMware VMotion and adequate for enterprise data centers, even though Quick Migration is not true live migration. We’ve even heard Microsoft tell audiences that our customers don’t trust VMotion enough for production use. Don’t fall for it — VMotion is ready, proven and in heavy use today by VMware customers who are bringing true flexibility and agility to their IT operations.

Do you remember the many grand visions for IT that were trotted out by the vendors and analysts during the dot com boom times? Adaptive Enterprise Computing, Next Generation Data Centers, Organic IT, On-demand Computing, Utility Computing and more were relentlessly pitched to CIOs with PowerPoint promises of continuously available services effortlessly floating on pools of servers and storage, finding the resources they needed all by themselves and magically recovering from any faults and disasters that should arise.  CIOs put up with the daydreaming until the vendors were finally shamed into backing off on the hard sell by their noticeable inability to deliver on the promises. The technology, especially in the x86 world, just could not break the bonds that kept applications and services firmly welded to their physical hosts.

The phenomenal growth of virtualization is now reviving some of those grand IT visions. With a virtualization layer that includes live migration, x86 workloads can float free of the fixed servers and storage hardware that enterprises have in place. And, thanks to tools like VMware VMotion that live migrates servers between hosts and VMware Storage VMotion that allows transparent relocation of a VM’s storage, those workloads finally can accomplish that floating without the slightest interruption to users and services. It’s not just VMware that is enabling this revolution-in-waiting; the Xen vendors are also starting to roll out their own live migration support.

It should not be surprising then, that Microsoft is using its entry into the virtualization market to bring its own grand architecture – the dormant “Dynamic Systems Initiative” – out of hibernation. Now apparently renamed as “Dynamic IT,” their vision was featured in Bob Muglia’s January 21 V-day missive to hundreds of thousand of Microsoft customers and partners.  In laying out the benefits of virtualization and live migration, we couldn’t have said it better ourselves:

"In the data center, virtualization not only supports server consolidation, but it enables workloads to be added and moved automatically to precisely match real-time computing needs as demand changes. This provides greater agility, better business continuity, and more efficient use of resources."

That “moved automatically” part sounds pretty compelling. Of course, you’d only want workloads to get up and move themselves if they could do so without the inconvenience of planned maintenance windows and application downtime. That’s exactly what VMware users have been doing with VMotion since we introduced it in 2003. VMotion delivers true live migration – users and services see no interruptions when a virtual machine is moved from one host to another. VMotion has proven so liberating and reliable that 59% of VMware customers use it regularly in production; some have accumulated hundreds of thousands of perfectly transparent migrations as VMs are automatically load balanced across host clusters with DRS. You don’t need to build a large-scale virtual infrastructure to benefit from VMotion. We see over and over how customers that adopt VMware Infrastructure for basic server consolidation projects quickly come to rely on the agility and freedom of VMotion as an essential element of their IT operations.  Here’s what Qualcomm had to say about the flexibility provided by VMotion:

"We’ve utilized VMotion extremely heavily. It offers so many benefits: being able to deal with downtimes, being able to do maintenance on the hardware supporting ESX Server hosts, and being able to balance resources. VMotion is a must-have capability for anyone seriously thinking of deploying virtual infrastructure."

While we’re gratified to see virtualization taking the lead in reviving Microsoft’s DSI story, its own virtualization tools are missing the crucial live migration support needed to pull it off. It’s important to know that Microsoft dropped plans for live migration in Hyper-V and is relying on a “not quite live” migration method it calls, “Quick Migration.” Microsoft Quick Migration works very differently than the iterative live memory transfer method used by VMware VMotion. Quick Migration fully suspends a VM, copies its memory image to disk, and then reloads and resumes the VM on a new host. That suspend/resume migration technique is far from live. In fact, Microsoft has documented (slide 47) that, even in ideal conditions, Quick Migration interrupts VMs between eight seconds and two minutes when using Gigabit speed networked storage, depending on VM memory size.

MSFT_Quick_Migration_slide_794x595

Unfortunately, that kind of downtime is more than most networked applications can tolerate. Just a few seconds of unresponsiveness will trigger TCP timeouts and application errors. We tried Quick Migration with the Hyper-V beta using Gigabit iSCSI storage connections and the results weren’t pretty, as you can see in this screen capture video:

(Clicking the screen icon Picture_1 switches to full screen mode, which will make the window text legible. If that doesn’t work, you can go directly to this movie at blip.tv)

The Quick Migration downtime caused file copies to fail, VM console connections were severed, and database clients had to be restarted. Scheduling planned maintenance downtime and telling users their apps will be down does not fit anyone’s definition of “Dynamic IT.” In contrast, migrating the same VM with VMotion on a VMware Infrastructure platform didn’t cause even a blip in the network sessions as this video shows:


(Clicking the screen icon Picture_1_2 switches to full screen mode, which will make the window text legible. If that doesn’t work, you can go directly to this movie at blip.tv)

Lab_arch_hyperv_5

In anticipation of any concerns that we stacked the deck in this demo to cause Quick Migration failures, we were careful to configure our Hyper-V setup exactly as documented in this Microsoft TechNet article (it was the only documentation on Quick Migration configuration we could find.)  We also used the latest Windows Server 2008 RTM and Hyper-V RC0 releases.  We’ve been repeating this Quick Migration test all the way back to the Viridian CTP release and with Virtual Server 2005 R2 before that, and we’ve always seen the same network session failures every time. Here’s a diagram of our Win2008/Hyper-V setup shown on the right.

I encourage any readers who’ve tried their own Quick Migration tests to share their experiences.

If you’re wondering why Quick Migration of a VM exhibits these network failures, but a normal Microsoft Cluster Service failover keeps network sessions alive, take a look at Mike DiPetrillo’s excellent explanation.  It’s due to the fact that during the time it takes to suspend then resume a quick migrating VM, there’s no network stack available to respond to its IP address.  Mike also explains how VMotion preserves network connections and shows how VMotion has become an indispensable money-saver for VMware customers.

While Microsoft may not be ready to deliver the true live migration needed for Dynamic IT in Hyper-V, their customers don’t need to defer their dreams of automated workload migrations and resource balancing. Microsoft operating systems and applications run great in VMware virtual machines and users can take full advantage of powerful virtualization services like VMotion, DRS, HA, Consolidated Backup, Storage VMotion and Update Manager. Live migration is finally letting Dynamic IT and all the other grand architectures of IT live up to their promises of data center agility and hardware independence.  Customers just need to ensure they choose a virtualization technology that supports true live migration like VMware VMotion and not get trapped with an inadequate substitute.

Yankee Group rescinds own report, but Microsoft continues to distribute it…

VMware met with Yankee Group to provide our feedback on the factual inaccuracies in the report "Virtualization Price War: VMware’s Little Big Horn?". We did this around the same time we put up our blog posting summarizing the issues point-by-point. Yankee Group understood our concerns, agreed to do a revision to address the issues, and promptly took down the original report from its website several weeks ago.

Because of the factual inaccuracies in the report, Yankee Group also committed to requesting that Microsoft, who had purchased distribution rights to the report, cease distributing the original report. However, three weeks after our discussion with Yankee Group and three weeks after Yankee Group pulled the report from its website, Microsoft still continues distributing the report, such as in the Microsoft Virtualization Newsletter that just went out on 4/2/2008.

I wonder why Microsoft would continue distributing a report as marketing material, when the author, Yankee Group has rescinded the report…