perform I/O to the disk directly, which is the most common activity when dealing with
virtual hard disks. However, no namespace/Metadata changes can be made by
noncoordinator nodes; for example, when creating, deleting, resizing, and opening
files. These operations require management of the NTFS filesystem structure, which
is carefully controlled by the coordinator node to avoid corruption. Fortunately, these
types of actions are relatively rare, and when a noncoordinator node needs to perform
such an action, it forwards the action via SMB to the coordinator node that then
makes the namespace changes on its behalf, since the coordinator has the NTFS
locally mounted and thus has full Metadata access. This is shown in action in Figure
7.28, where a single node is acting coordinator for both disks.
Figure 7.28 Cluster Shared Volume normal operation
The CSV technology provides another useful feature. If a noncoordinator node loses
Direct Access to the LUN—for example, its iSCSI network connection fails—all of its
I/O can be performed over SMB via the coordinator node using the cluster network.
This is known as redirected I/O, and it is shown in Figure 7.29.