A fast snap is a consistent point-in-time copy or logical copy of a storage object that can be created more quickly than an ordinary snap. In order to generate a fast snap a storage array creates a copy or logical copy of all of the dirty data associated with a source device by copying or logically copying dirty pages cache into a separate record in volatile memory, instantiates an unpopulated snap device that is backed by persistent storage, and generates a mapping between the record and the unpopulated snap device. The mapping includes the information needed to populate the unpopulated snap device with the dirty pages from the record. Once the fast snap has been created it is possible to service IOs to the source device and the fast snap device because the data can be accessed from the record and the cache.