No. 7 (00072)

Family name : Domenici
Given name : Andrea
Affiliation : University of Pisa and INFN Pisa
Abbreviation : 
E-mail address : Andrea.Domenici@iet.unipi.it
Title : REPLICA CONSISTENCY IN A DATA GRID
Authors : A. Domenici, F. Donno, K. Paschen, G. Pucciani, H. Stockinger,
          K. Stockinger
Abstract : 
A Data Grid is a wide area network that employs Grid technologies to
provide storage capacity and processing power to applications that
handle very high quantities of data.  Data Grids rely on data
replication to achieve better performance and reliability by storing
copies of data sets on different Grid nodes.  When a data set can be
modified by applications, the problem of maintaining consistency among
the existing copies arises.

The consistency problem also concerns metadata, i.e., additional
information about application data sets such as indices, directories, or
catalogs. This kind of metadata is used both by the applications and by
the Grid middleware to manage the data.  For instance, the Replica
Management Service (the Grid middleware component that controls data
replication) uses catalogs to find the replicas of each dataset.  Such
catalogs can also be replicated and their consistency is crucial to the
correct operation of the Grid.  Therefore, metadata consistency
generally poses stricter requirements than data consistency.

In this paper we report on the development of a Replica Consistency
Service based on the middleware mainly developed by the European Data
Grid Project. The paper summarizes the main issues in the replica
consistency problem, defines the requirements of specific data-intensive
applications, and lays out a high-level architectural design for a
Replica Consistency Service.  Finally, results from simulations of
different consistency models are presented.