6.4 vSAN Storage Policy Design
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 example, 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 will automatically be 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. Finally, all virtual machines created on vSAN will be thin-provisioned, so plan accordingly to avoid overcommitting resources.