Live Migration uses the new Cluster Shared Volumes (CSV) feature within Failover Clustering in Windows Server 2008 R2. The CSV volumes enable multiple nodes in the same failover cluster to concurrently access the same logical unit number (LUN). From a VM’s perspective, each VM appears to actually own a LUN; however, the .vhd files for each VM are stored on the same CSV volume, as illustrated in the following figure.
Figure 3: Cluster Shared Volumes
Because CSV provides a consistent file namespace to all nodes in the cluster, any files stored on a CSV have the same name and path from any node in the cluster. CSV volumes are stored as directories and subdirectories beneath the ClusterStorage root folder, as illustrated in the following figure.
Figure 4: Example of single namespace in CSV
As illustrated in the previous figure, the CSV volumes (Volume1, Volume2, and Volume3) are stored in the ClusterStorage folder. If the ClusterStorage folder exists in the root of E:, the fully qualified path to each of the CSV volumes would be as follows:
E:\ClusterStorage\Volume1\root
E:\ClusterStorage\Volume2\root
E:\ClusterStorage\Volume3\root
All cluster nodes would access the shared volumes by using these fully qualified paths.
While CSVs are currently employed mainly for Live Migration, their benefits will extend beyond that single scenario. For one, they’re easy to configure using simple NTFS rather than some other proprietary format. That means administrators won’t have to reformat their SANs to take advantage of CSVs. It also means administrators will have an easier time showing users only a single data repository rather than a small forest of silos—no more drive letter metaphors for end-users just convenient networked storage. And last, CSVs don’t require config and management tools of their own. Windows Server administrators used to the tools in Windows Server 2008 can continue using those same consoles and they’ll simply work with CSVs in R2.
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