On top of the live virtual machine migration, automated load balancing, and high-availability capabilities explored in our main article, VMware Infrastructure 3 has a number of other features that will be important to IT. Here's a rundown:
VM snapshotting This key feature enables admins to take live snapshots of the current disk and RAM contents of a server and store them. You can use a snapshot to back up the server without running into file locking problems, or to run before major system updates are applied, ensuring that the server can be brought back to a known good state in seconds. VI3 adds the ability to manage multiple snapshots of a single server, where ESX 2.5 could handle only one at a time. Snapshotting is an invaluable tool that makes major changes to running servers much less threatening. The only downside we discovered is that no confirmation dialogue appears when reverting to a snapshot. If you happen to click the button, you’ve just sent your server back in time. Also, when running iSCSI LUNs in Virtual Compatibility mode, taking a snapshot of a server with an iSCSI LUN attached will result in a VI3 snapshot encompassing the LUN. This action is configurable, but the default is to handle the snapshot in this manner.
VM cloning and templating With these new tools, a single VM can be built and configured, then converted to a template for use in manual or automatic VM creation. For Windows Server 2003 and 32-bit operating systems, VMware offers customization tools that will handle Sysprep on the Windows servers and IP/hostname changes on the Linux VMs that are built from a template. Thus, with a single “gold” template of a production server, multiple clones can be built with a few mouse clicks, with each cloned VM receiving a unique identity, name, IP address, and so forth. When coupled with customized actions in response to alarms and the VirtualCenter scripting API, it’s possible to completely automate the addition of new servers into a Web farm when load increases, for instance. In one customer case that VMware highlighted, when the load on existing Web server VMs passes a certain point a set of custom scripts and alarm configurations will build new Web servers from a gold template, add an entry into the load balancer, and inform admins that the action occurred. All the BlackBerry-carrying server admins sitting around the console in the Fergenschmeir datacenter looked at one another and instantly flashed on the server failures caused by a recent weekend Slashdotting and the subsequent reduction in their opportunity to spend that weekend drinking beer on a floaty in the pool.
Cloning is subject to the same LUN mapping surprise as snapshotting. On a file server with a 4GB local disk and a 400GB iSCSI volume, this results in a 404GB snapshot, which can be inconvenient to say the least. Again, this is customizable, but the default is to clone every disk. Also, the lack of customization support for 64-bit Linux servers and some more recent OS releases is perplexing and should be remedied, especially given the relative ease of the operation.
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