Typically, I/O filters are created by VMware partners through the vSphere APIs for I/O Filtering (VAIO) developer program. Third-party vendors can develop I/O filters for multiple purposes.
In this release, the supported types of filters include the following:
Caching. Implements a cache for virtual disk data. The filter can use a local flash storage device to cache the data and increase the IOPS and hardware utilization rates for the virtual disk. If you use the caching filter, you might need to configure a Virtual Flash Resource.
Replication. Replicates all write I/O operations to an external target location, such as another host or cluster.
You can install several filters from the same category, such as caching, on your ESXi host. However, you can have only one filter from the same category per virtual disk.