Cisco and VMware have created a method for using VMware's VMotion across data centres that are located as far as 200 kilometres (125 miles) apart.
Users have been pushing VMware to offer a method of allowing VMotion to be used between data centres, and this reference architecture is a step in the right direction. But it is only a step and not a true failover technology. It does not replace VMware's disaster recovery product, Site Recovery Manager.
The long-range Vmotion technique was originally demonstrated at Cisco Live! But VMware formally announced support for it. It can be used with Cisco switches that support VLANs, namely the Catalyst 6500 as well as the Nexus 7000. It requires that users implement VMware's latest product, vSphere.
Today's announced reference design provides only what its makers refer to as "disaster avoidance" not "disaster recovery." Long-range movement of a virtual machine using VMotion must be performed manually (although users could write scripts to move VMs.)
Technical issues with the network and storage have yet to be solved to allow VMotion to support more automated long-distance failover. These include an inability to maintain an IP address if a VM is moved from one ISP to another, for instance from a data centre in New York to another in San Jose. Likewise, storage is a problem. Until storage vendors come up with a way to support active/active SANs for the same VM moved between two physically far locations, no-latency failovers won't be possible between data centres.
Finally, this technique is not recommended, and not supported by VMware, when users have Disk Raw Mapping (DRM) turned on and used with clustered servers on either side.
All that said, for Cisco users wanting to deploy vSphere, this design can be practical in helping them manage VMs between data centres. It can be used for disaster situations where users have warning (tornadoes, hurricanes). It can be helpful for load balancing applications between data centres to offset an expected traffic spike. It also represents major progress on the network portion of the long-range VMotion problem.
The reference architecture is available for free download from Cisco.
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