As you might have noticed last week I’m still digesting all the info from VMworld. One of the coolest new supported technologies is Long Distance VMotion. A couple of people already wrote a whole article on this session so I will not be doing this. (Chad Sakac, Joep Piscaer) However I do want to stress some of the best practices / requirement to make this work.
- An IP network with a minimum bandwidth of 622 Mbps is required.
- The maximum latency between the two VMware vSphere servers cannot exceed 5 milliseconds (ms).
- The source and destination VMware ESX servers must have a private VMware VMotion network on the same IP subnet and broadcast domain.
- The IP subnet on which the virtual machine resides must be accessible from both the source and destination VMware ESX servers. This requirement is very important because a virtual machine retains its IP address when it moves to the destination VMware ESX server to help ensure that its communication with the outside world (for example, with TCP clients) continues smoothly after the move.
- The data storage location including the boot device used by the virtual machine must be active and accessible by both the source and destination VMware ESX servers at all times.
- Access from VMware vCenter, the VMware Virtual Infrastructure (VI) management GUI, to both the VMware ESX servers must be available to accomplish the migration.
- Create HA/DRS Clusters on a per site basis. (Make sure I/O stays local!)
- A single vDS (like the Cisco Nexus 1000v) across clusters and sites.
- Network routing and policies need to be synchronized or adjusted accordingly.
Most of these are listed in this excellent whitepaper from VMware, Cisco and EMC by the way.
Combining this current available technology with what Banjot discussed during his VMworld session regarding HA futures I think the possibilities are endless. One of the most obvious ones is of course Stretched HA Clusters. When adding VMotion into the mix a stretched HA/DRS Cluster would be a possibility. This would require other thresholds of course but how cool would it be if DRS would re-balance your clusters based on specific pre-determined and configurable thresholds?!
Stretched HA/DRS Clusters would however mean that the cluster needs to be carved into sub-clusters to make sure I/O stays local. You don’t want to run your VMs on site A while their VMDKs are stored on site B. This of course depends on the array technology being used. (Active / Active, as in one virtual array would solve this.) During Banjot session it was described as “tagged” hosts in a cross site Cluster and during the Long Distance VMotion session it’s described as “DRS being aware of WAN link and sidedness”. I would rather use the term “sub-cluster” or “host-group”. Although this all seems to be still far away it seems to be much closer than we expect. Long Distance VMotion is supported today. Sub-clusters aren’t available yet but knowing VMware, and looking at the competition, they will go full steam ahead.