ConVirt: the New Tool in Your Virtual Toolbox
Provisioning from CD is nice for custom machines or one-off builds, but if you have to spin up multiple guests at once, it is a very inefficient method. It is much more efficient to create a single VM and clone it over and over again, which is possible in ConVirt. To demonstrate this method of provisioning, I created a pristine (or "golden") image of a Windows XP machine. This VM contains all of the settings and software needed so that I don't need to make changes to each new VM that is spun up. After the golden image is ready, power it down in the hypervisor or ConVirt, and copy the guest's .xm file to a separate location. In my case, I copied it to an NFS share mounted on the ConVirt and all of my managed servers. You then need to gzip your .xm image in its new location to give it a .gz extension. Next, copy the Windows CD template by right-clicking it in the templates section and clicking on the Create Like option.
You could create a template from scratch, but copying and modifying a built-in one is just as quick. If you have very custom settings that differ greatly from those found in the pre-built templates, that may be the way to go.
When prompted, give your template a new name. Once the new template appears in the list, right-click on it and select the Edit Settings option. Click on the Storage option and remove the existing storage defined for hda. Click on the New button at the top of the window. On the resulting window, set the Option field to Clone Reference Disk. Change the Ref. Disk Type to Disk Image and the Ref. Format to .gzip. In the Ref Loc. field, browse or enter the path to your .iso file. Change the VM Device: field to "hda". Your settings should resemble those shown in Figure 7.
Figure 7. Provisioning Settings to Clone the Golden Image
To deploy a new cloned VM from this template, right-click it and select Provision. With the reference disk method, ConVirt will copy the .gz file to its destination and expand it to the desired size of the new VM. What is really nice is that you can specify a larger disk size than the one inside your golden image. On my XP VMs, the space automatically was added to the guest partition (not usually an easy task). It is a common best practice to keep your golden image as small as possible to fit as many different size drives (virtual or physical) that you will deploy it to.
After your deployment is in place, you may find that you need to move guests to another host to balance loads between servers, to move a VM from one network site or segment to another or to perform maintenance on a host with zero downtime to running guests. VMware dominated the market for years with its vMotion feature that performs this task well. ConVirt provides this same operation.
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