VMware provides certain categories of I/O filters that are installed on your ESXi hosts. In addition, VMware partners can create the I/O filters through the vSphere APIs for I/O Filtering (VAIO) developer program. The I/O filters can serve multiple purposes.
The supported types of filters include the following:
Replication. Replicates all write I/O operations to an external target location, such as another host or cluster.
Encryption. Offered by VMware. Provides encryption mechanisms for virtual machines. For more information, see the vSphere Security documentation.
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.
Storage I/O control. Offered by VMware. Throttles the I/O load towards a datastore and controls the amount of storage I/O that is allocated to virtual machines during periods of I/O congestion. For more information, see the vSphere Resource Management documentation.
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.