Elastic Quotas


Despite seemingly endless increases in the amount of storage and ever decreasing costs of hardware, managing storage is still expensive. Additionally, users continue to ?ll increasingly larger disks, worsened by the proliferation of large multimedia ?les and high-speed broadband networks. Storage requirements are continuing to grow at a rate of 50% a year. Worse, existing hard disk technology is reaching physical limitations, making it harder and costlier to meet growing user demands .
Storage management costs have remained a signi?cant component of total storage costs. Even in the ?70s, storage costs at IBM were several times more than hardware costs, and projected that they would reach ten times the cost of the hardware. Today, anagement costs are ?ve to ten times the cost of underlying hardware and are actually increasing as a proportion of cost ecause administrators have a limited amount of storage each can manage. Up to 47% of storage costs are associated with administrators manually manipulating ?les. Thankfully, signi?cant savings are possible: studies show that over 20% of all ?les--representing over half of the storage--are regenerable . Other studies, indicate that 82%-85% of storage is allocated to ?les that have not been accessed in more than a month.

The studies shows that storage management has been a problem in a past, continues to be a problem today, and is only getting worse--all despite growing disk sizes. Recent trends have begun to address the management of storage through virtualization . Morris put forth the idea of Autonomic Computing,which includes "the system?s ability to adjust to its con?guration and resource allocation to achieve predetermined goals". Elastic Quota system is designed to help the management problem via ef?cient allocation of storage while allowing users maximal freedom, all with minimal administrator intervention. Elastic quotas enter users into an agreement with the system: users can exceed their quota while space is available, under the condition that the system will be able to automatically reclaim the storage when the need arises. Users or applications may designate some ?les as elastic. When space runs short, the elastic quota system (Equota) may reclaim space from those ?les marked as elastic; nonelastic ?les maintain existing semantics and are accounted for in users? persistent quotas .

This report focuses on policies for elastic space reclamation and is organized as follows. Section 2 describes the overall architecture of the policy system. Section 3 discusses the various elastic quota policies. In Section 4 we discuss nteresting implementa tion aspects of Elastic Quota.Secrion 5 presents measurements and performance results of various policies. Section 6 discusses work related to storage space management policies. Finally, Section 7 presents some concluding remarks and directions for future work.




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