To prevent resource (especially storage) shortage, information systems such as storage services and email services usually impose an upper bound of resource consumption (quota) per user. In a conservative way, an administrator tends to set a quota value such as the storage capacity divided by the expected maximum number of users for safety and fairness, but it tends to leave large unused storage space, because the users' storage usage pattern shows a long-tailed distribution. In this paper, we analyzed storage usage distribution of some email services to approximate the distribution using a power-law distribution, and proposed a method to calculate an optimal quota value from a target size of storage consumption to increase storage utilization. We applied an optimal quota value we calculated to a real email service and analyzed the effect of quota change. Then, we analyzed actual distributions further to find a better model to approximate the distribution, and found that a log-normal distribution explained the distribution better than power-law. We also analyzed two other universities' email service to find similar distribution in these systems.
['Yoshiaki Kasahara', 'Takuya Kawatani', 'Eisuke Ito', 'Koichi Shimozono']
An Analysis of Relationship between Storage Usage Distribution and Per-User Quota Value