Last week, I wrote about the huge benefits and associated challenges of implementing "stretched" virtualization clusters. These offer tangible benefits over traditional hot/warm site implementations in that they allow workloads to be seamlessly migrated from one site to the other. In some cases, they even allow site fail-over to take place automatically.
But the expense of clustered storage -- not to mention the complexity involved -- put true stretched clusters out of reach for many organizations that could benefit from them. In spite of that, even if you don't have the right kind of back-end storage to implement a true stretched cluster, you may still be able to reap some of the flexibility benefits they bring to the table and ease the heavy lifting of complex upgrades and stringent uptime requirements.
Recently, I found myself faced with the prospect of upgrading a sizable dual-site virtualization infrastructure. Though each upgrade taken individually wasn't that complicated, a strict zero-downtime requirement meant that careful planning would be required. In the end, the solution leveraged many of the same concepts present in stretched clusters, illustrating that you can enjoy some of the benefits without having all of the pieces in place.