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Definition
Despite seemingly endless increases in the amount
of storage and ever decreasing costs of hardware, managing storage is still expensive.
Additionally, users continue to fill increasingly larger disks, worsened by the
proliferation of large multimedia files 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 significant
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, management costs are five to ten times
the cost of underlying hardware and are actually increasing as a proportion of
cost because administrators have a limited amount of storage each can manage.
Up to 47% of storage costs are associated with administrators manually manipulating
files . Thankfully, significant savings are
possible: studies show that over 20% of all files--representing over half of the
storage-are regenerable . Other studies, indicate that 82%-85% of storage is allocated
to files 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 configuration and resource allocation to achieve predetermined
goals" . Elastic Quota system is designed to help the management problem
via efficient allocation of storage while allowing users maxi-mal 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 re-claim the storage when the need arises. Users or applications
may designate some files as elastic. When space runs short, the elastic quota
system (Equota) may reclaim space from those files marked as elastic; nonelastic
files 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
interesting implementation aspects of Elastic Quota. Section 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. Design
The primary design goals were to allow for versatile and efficient elastic quota
policy management. An additional goal was to avoid changes to the existing OS
to support elastic quotas. To achieve versatility the Elastic Quota system is
designed with a flexible policy management configuration language for use by administrators
and users; a number of user-level and kernel features exist to support this flexibility.
To achieve efficiency the design allows the system to run as a kernel file system
with DB3 databases accessible to the user-level tools. Finally, the design uses
a stackable file system to ensure that there is no need to modify existing file
systems such as Ext3 . <<back |