Extending DIRAC File Management with Erasure-Coding for efficient storage

TL;DR

This paper extends the Dirac File Catalogue to support erasure-coded files, improving storage efficiency and data resilience by distributing files across multiple endpoints with error correction, while analyzing costs and benefits.

Contribution

It introduces a transparent erasure-coding extension to Grid file management, enhancing storage efficiency and parallel data access capabilities.

Findings

Erasure coding reduces storage overhead compared to replication.

Parallel access to distributed chunks improves data transfer performance.

Overheads for multiple file transfers are a current challenge.

Abstract

The state of the art in Grid style data management is to achieve increased resilience of data via multiple complete replicas of data files across multiple storage endpoints. While this is effective, it is not the most space-efficient approach to resilience, especially when the reliability of individual storage endpoints is sufficiently high that only a few will be inactive at any point in time. We report on work performed as part of GridPP\cite{GridPP}, extending the Dirac File Catalogue and file management interface to allow the placement of erasure-coded files: each file distributed as N identically-sized chunks of data striped across a vector of storage endpoints, encoded such that any M chunks can be lost and the original file can be reconstructed. The tools developed are transparent to the user, and, as well as allowing up and downloading of data to Grid storage, also provide the possibility of parallelising access across all of the distributed chunks at once, improving data transfer and IO performance. We expect this approach to be of most interest to smaller VOs, who have tighter bounds on the storage available to them, but larger (WLCG) VOs may be interested as their total data increases during Run 2. We provide an analysis of the costs and benefits of the approach, along with future development and implementation plans in this area. In general, overheads for multiple file transfers provide the largest issue for competitiveness of this approach at present.