Home // International Journal On Advances in Telecommunications, volume 10, numbers 3 and 4, 2017 // View article

Reliability Evaluation of Erasure Coded Systems

Authors:
Ilias Iliadis
Vinodh Venkatesan

Keywords: Reliability metric; MTTDL; EAFDL; RAID; MDS codes; Information Dispersal Algorithm; Prioritized rebuild.

Abstract:
Replication is widely used to enhance the reliability of storage systems and protect data from device failures. The effectiveness of the replication scheme has been evaluated based on the Mean Time to Data Loss (MTTDL) and the Expected Annual Fraction of Data Loss (EAFDL) metrics. To provide high data reliability at high storage efficiency, modern systems employ advanced erasure coding redundancy and recovering schemes. This article presents a general methodology for obtaining the EAFDL and MTTDL of erasure coded systems analytically for arbitrary rebuild time distributions and for the symmetric, clustered, and declustered data placement schemes. Our analysis establishes that the declustered placement scheme offers superior reliability in terms of both metrics. The analytical results obtained enable the derivation of the optimal codeword lengths that maximize the MTTDL and minimize the EAFDL. It is theoretically shown that, for large storage systems that use a declustered placement scheme, both metrics are optimized when the codeword length is about 60% of the storage system size.

Pages: 118 to 144

Copyright: Copyright (c) to authors, 2017. Used with permission.

Publication date: December 31, 2017

Published in: journal

ISSN: 1942-2601