Several vendors have deployed this technology in the form of a snapshot or copy-on-write feature for point-in-time copies. This allows customers to save big on storage purchases made for replica copies. The underlying premise is that change rates are never more than 20% to 30%. If you apply this concept to your primary storage, this suddenly becomes an interesting way to overprovision. But what happens if a host (or a set of hosts) suddenly needs more space? Again, there's a solution. If you pool all of the resources into a single bucket (often known as the resource pool), then any server or set of servers can borrow against its allocated resources on an as-needed basis.