"The technology that delivers the most benefits for business but causes the most headaches for operation is virtual machine live migration," writes Andreas Antonopoulos of Nemertes in a post titled "Dude, where's my server?" An excerpt:
Live migration, also known as VMotion or XenMotion in the VMWare and Xen products respectively allows you to move virtual machines from physical server to physical server without any discernible interruption. ... Wonderful features for business agility. But by making virtual machines mobile this feature makes troubleshooting even harder. Add the other features and you might have machines moving around automatically and constantly.
Andreas notes that tracking and managing VMs is critical to trouble-shooting. Moving virtual machines from server to server within a data center creates another challenge: as the computing load migrates, so does the heat load. A box that is underutilized one minute can become a high-density server in short order.
Live migration is one more technology that demonstrates the need for close cooperation between IT and facilities, and places a premium on monitoring and dynamic data center management. In most data centers, hot spots are difficult enough to manage when they're standing still.