When you provision a virtual machine on a datastore, you must assign to the virtual machine a compatible VM storage policy. If you do not configure and explicitly assign the storage policy to the virtual machine, the system uses a default storage policy.

VMware-Provided Default Storage Policy
The generic default storage policy that ESXi provides applies to all datastores and does not include rules specific to any storage type.

In addition, ESXi offers the default storage policies for object-based datastores, vSAN or vVols. These policies guarantee the optimum placement for the virtual machine objects within the object-based storage.

For information about the default storage policy for vVols, see vVols and VM Storage Policies.

VMFS and NFS datastores do not have specific default policies and can use the generic default policy or a custom policy you define for them.

User-Defined Default Storage Policies
You can create a VM storage policy that is compatible with vSAN or vVols. You can then designate this policy as the default for vSAN and vVols datastores. The user-defined default policy replaces the default storage policy that VMware provides.

Each vSAN and vVols datastore can have only one default policy at a time. However, you can create a single storage policy with multiple placement rule sets, so that it matches multiple vSAN and vVols datastores. You can designate this policy as the default policy for all datastores.

When the VM storage policy becomes the default policy for a datastore, you cannot delete the policy unless you disassociate it from the datastore.