The SAN also needed to be resized and rebalanced for the steeper failover I/O in a virtual-server environment. The issue, Hilton says, is that a dozen server images take a lot of storage and I/O all at once if their physical server fails and they need to be moved. Essentially, there's a price to be paid in the SAN infrastructure to support the higher density of multiple VMs on a physical server.
The other deployment strategy Hilton needed to work out involved the ongoing provisioning and maintenance of the virtual servers: "It's so easy to provision a VM, so how do you ensure that an enterprise doesn't create them willy-nilly?" Credit Suisse's solution was to automate the provisioning. All requests go to a central tool that tracks the requests, available resources, and so forth, so IT can track usage easily and be alerted when potentially abusive requests occur, such as multiple VMs requested by the same person or department in a short period. Essentially, the VM and the resources that they reside in are treated as inventory to be managed.
The automated system also let Hilton introduce the concept of leasing VMs to developers. "They get it for 30 days, then it disappears. Otherwise, it would live forever, as it did with physical servers. You can't be a box-hugger any more," he says.