I/O filters that are associated with virtual disks gain direct access to the virtual machine I/O path regardless of the underlying storage topology.
VMware offers certain categories of I/O filters. In addition, the I/O filters can be created by third-party vendors. Typically, they are distributed as packages that provide an installer to deploy filter components on vCenter Server and ESXi host clusters.
When I/O filters are deployed on the ESXi cluster, vCenter Server automatically configures and registers an I/O filter storage provider, also called a VASA provider, for each host in the cluster. The storage providers communicate with vCenter Server and make data services offered by the I/O filter visible in the VM Storage Policies interface. You can reference these data services when defining common rules for a VM policy. After you associate virtual disks with this policy, the I/O filters are enabled on the virtual disks.
See vSphere Storage for more information.