Q. If I'm using VMware virtualization technologies, what are the network requirements to use vMotion?

A. During a vMotion operation, the memory of the virtual machine (VM) is copied to the target host. Then iterative copies are performed of memory pages that have changed during the previous copy. vMotion has no hard limit on the number of times it copies dirty memory, but obviously each iteration has less to copy, so a finite number of cycles should be required.

Once the amount of memory copies drops below the amount that can be sent in less than a certain time (0.5 seconds), the VM is frozen and remaining memory is copied over along with partition state. You normally see two to three iterations of memory copy. For very active VMs, you could see four to five iterations.

For your network, you want a dedicated gigabit network (in fact, 10Gb is supported) just for the vMotion traffic for two main reasons. Firstly, so that the bandwidth is available to copy the memory as quickly as possible without conflicts. Secondly, because you're copying memory that may contain sensitive information, it's good to segregate this traffic from other network traffic for security reasons. No other types of port are required on the vMotion switch (like Service Console). Technically, if you have very small VMs (such as a 500MB VDI), you may be able to use a 100Mb link, but this isn't recommended given the time taken to copy the memory.

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