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Monthly Archives: October 2011

The vMotion Speed Advantage: It’s Real, and It’s Spectacular

The raw speed of VMware vMotion live migrations for moving single and multiple virtual machines has been a huge timesaver for our customers. Speedy concurrent vMotions let system administrators quickly evacuate the VMs off hosts before a planned server maintenance session so they can get home on time, rather than spending extra hours at work to swap a server power supply or do a firmware upgrade. vMotion also has a minimal impact on VM performance, so mission-critical VMs can be moved during production hours without generating user complaints.

vSphere 4.1 introduced support for up to eight concurrent vMotion migrations per host and 10Gb vMotion networks. vSphere 5 boosted the raw speed of each vMotion over 1Gb and 10Gb networks and added the ability to utilize multiple network links. Now, thanks to independent lab tests conducted by Principled Technologies, we can show just how fast vMotion operates.

Principled Technologies compared vSphere 5 vMotion performance to live migrations conducted with Microsoft Windows Server 2008 Hyper-V R2 SP1. The comparison to Hyper-V was of special interest to us because we’ve seen claims from those in the Hyper-V camp that allowing multiple concurrent vMotions couldn’t possibly be faster than Hyper-V’s one-at-a-time live migrations because Hyper-V can saturate a network link with its live migration memory copy traffic. The Hyper-V advocates discounted the advantages of concurrent vMotions, arguing that they would be bottlenecked by the network.

The results of the Principled technology tests show those arguments are flat wrong. Using identical hosts connected over a single 10Gb network link, a host evacuation simulation where 10 VMs running SQL Server were migrated between hosts showed that vMotion completed the task 5.4 times faster than Hyper-V. vSphere reached its peak capacity of eight of simultaneous vMotions during the test, proving the benefits of concurrent live migrations.

PT_Live_Migration_Fig3

Principled Technologies then looked at live migration of a typical large Tier-1 application. Their test migrated a single 16GB, 4 CPU VM running a heavily loaded SQL Server database. Customers might shy away from such a demanding live migration during production hours. However, the results from Principled Technologies show that vSphere 5 users can migrate Tier-1 apps with confidence, but Hyper-V system administrators might want to plan on some late-night overtime. vMotion migrated the large VM 3.4 times faster than Hyper-V.

 

PT_Live_Migration_Fig4

Maybe more importantly, vMotion’s shorter migration window minimized the impact of live migration on application performance. Compared to a Hyper-V live migration that disrupted the SQL application with long periods of zero throughput, the vMotion VM was able to process 63% more transactions during the migration window.

PT_Live_Migration_Fig5 PT_Live_Migration_Fig6

 

Please take a look at the full test report from Principled Technologies to get the complete test details as well as their findings that vMotion showed perfect reliability, but Hyper-V live migrations resulted in occasional, but reproducible, VM blue screens. With differences like these, it’s no surprise that Microsoft is now talking about augmenting a future release of Hyper-V with concurrent live migration capabilities. As with so many other features that are vSphere exclusives, VMware customers will be enjoying their benefits, while Hyper-V users, waiting for Microsoft to deliver on promised enhancements sometime in the future, will be enviously glancing at them.