In Video on Demand (VoD) services, the demand for content items greatly changes daily, so reducing the server load at the peak time is an important issue for ISPs to reduce the server cost. To achieve this goal, we proposed to reduce the server load by multicasting popular content items to all users independently of actual requests as well as providing on-demand unicast delivery. In this solution, however, the hit ratio of pre-distributed content items is small, and a large-capacity storage is required at set-top box (STB). We might be able to cope with this problem by limiting the number of pre-distributed content items or clustering users based on the history of viewing. We evaluate the effect of these techniques using actual VoD access log data. We clarify that the required storage capacity at STB can be halved while keeping the effect of server load reduction to about 80% by limiting pre-distributed content items, and user clustering is effective only when the cluster count is about two.