An Analysis of Relationship between Storage Usage Distribution and Per-User Quota Value

Abstract

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 lognormal distribution explained the distribution better than powerlaw. We also analyzed two other universities' email service to find similar distribution in these systems.

The Past, Current, and Future of our Email Services in Kyushu University

“…This time we could secure enough budget to build a system powerful enough to support all members of Kyushu Univerisity, so there were few performance issues. We had started to study how to utilize limited storage space of information services more efficiently from 2014 [7], but for this system it was almost irrelevant because it had enough storage estimated to support more than 5 years worth messages for all users. This system was designed for 5-year lifetime (including 5-year hardware and spam/malware signature support), so we will need to replace the system before the end of 2018 unless we choose to extend the support.…”