In cloud computing environment, data owners usually host huge data on the cloud servers where clients access the data without knowing actual location. Due to this data outsourcing on un-trusted servers, efficient and reliable verification of the outsourced data becomes an open challenge in data security of cloud storage. Additionally, the integrity checking protocol must be efficient in order to save the verifier's cost. This triggered huge set of research activities, resulting in amount of proposals. Integrity verification of client data is achieved commonly by using a technique called Provable Data Possession (PDP). This paper provides overview of current variations in PDP technique by specifying models, functionality, strengths and weaknesses.