After vSAN is enabled and configured, storage policies that define the virtual machine storage characteristics must be created. These characteristics allow configuration of different levels of service to be provided to a virtual machine. If no specific policy is applied, a default policy tolerating a single failure and having a single disk stripe is applied. Creating multiple policies with vSAN allows for policies to be applied on a per virtual machine basis and changed as needed.

As discussed earlier, vSAN is an object storage technology. Each virtual machine deployed on vSAN comprises a set of objects. VMDKs, snapshots, VM swap space, and the VM home namespace are all objects. Each of these objects is comprised of a set of components that are determined by capabilities configured in the VM storage policy. For instance, if a virtual machine is deployed with a policy to tolerate one failure, objects will be made up of two replica components. If the policy contains a stripe width, the associated object will be striped across multiple devices in the capacity layer. Each stripe is a component of the object.

As you plan the design with respect to component maximums, be aware that vSAN might decide that an object needs to be striped across multiple disks, even with the default policy of one stripe in place. Normally, this is the result of an administrator requesting that a VMDK be created that is too large to fit on a single physical drive. As previously highlighted, the maximum component size is 255 GB. To elaborate, objects that are greater than 255 GB in size are automatically divided into multiple components. For example, if an administrator deploys a 2-TB VMDK, it will result in eight or more components being created in the same RAID-0 stripe configuration.

vSAN guarantees the storage policies that have been configured. If a policy cannot be met, virtual machine provisioning fails, unless force provisioning has been set. Almost any combination of the possible attribute capabilities can be set in a policy. Some additional benefits of vSAN policy application include the ability to configure policies at any time and to switch policies “on-the-fly” for virtual machines.

Finally, all virtual machines created on vSAN will be thin-provisioned, so a design must deal with capacity management accordingly to avoid overcommitting resources. An understanding of the policies that can be set allows the administrator to avoid configuring policies that do not make sense.