6.7

Each Virtual Machine Executable (VMX) component of a virtual machine contains a Filter Framework that
manages the I/O filter plug-ins attached to the virtual disk. The Filter Framework invokes filters when the
I/O requests move between the guest operating system and the virtual disk. Also, the filter intercepts any
I/O access towards the virtual disk that happens outside of a running VM.
The filters run sequentially in a specific order. For example, a replication filter executes before a cache
filter. More than one filter can operate on the virtual disk, but only one for each category.
Once all filters for the particular disk verify the I/O request, the request moves to its destination, either the
VM or the virtual disk.
Because the filters run in user space, any filter failures impact only the VM, but do not affect the ESXi
host.
Storage Providers for I/O Filters
When I/O filters are installed on ESXi hosts, the I/O filter framework configures and registers a storage
provider, also called a VASA provider, for each host in the cluster.
Storage providers for I/O filtering are software components that are offered by vSphere. They integrate
with I/O filters and report data service capabilities that I/O filters support to vCenter Server.
The capabilities populate the VM Storage Policies interface and can be referenced in a VM storage policy.
You then apply this policy to virtual disks, so that the I/O filters can process I/O for the disks.
Using Flash Storage Devices with Cache I/O Filters
A cache I/O filter can use a local flash device to cache virtual machine data.
If your caching I/O filter uses local flash devices, you need to configure a virtual flash resource, also
known as VFFS volume. You configure the resource on your ESXi host before activating the filter. While
processing the virtual machine read I/Os, the filter creates a virtual machine cache and places it on the
VFFS volume.
vSphere Storage
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