This is a short post for those who are interested in deep technical details of one of the master architecture pieces introduced in the Enhanced Storage vMotion available in vSphere 5 Ent and Ent+ called Mirror Mode aka IO Mirroring. You can hear about the term in the Profile-Driven Storage video and the Storage DRS video. Mirror Mode can leverage VAAI and enable the use of copy off-load engines sometimes present in storage arrays making it even more appealing.
You can deep dive into Mirror Mode and the other available architectures by reading the The Design and Evolution of Live Storage Migration in VMware ESX written by Ali Mashtizadeh, Emre Celebi, Tal Garfinkel and Min Cai all from VMware.
We describe the evolution of live storage migration in VMware ESX through three separate architectures, and explore the performance, complexity and functionality trade-offs of each.