Calculating the I/O Cost of Linear Repair Schemes for RS Codes Evaluated on Subspaces via Exponential Sums

TL;DR

This paper introduces a method using exponential sums to calculate the I/O cost of linear repair schemes for Reed-Solomon codes, deriving bounds and designing schemes that optimize I/O and repair bandwidth.

Contribution

It presents a novel approach to compute Hamming weights via exponential sums, establishing lower bounds and constructing I/O-optimal repair schemes for RS codes with 2 or 3 parities.

Findings

Derived exact I/O cost bounds for specific RS code configurations.

Designed I/O-optimal repair schemes matching the bounds.

Achieved lower repair bandwidth for full-length RS codes with three parities.

Abstract

The I/O cost, defined as the amount of data accessed at helper nodes during the repair process, is a crucial metric for repair efficiency of Reed-Solomon (RS) codes. Recently, a formula that relates the I/O cost to the Hamming weight of some linear spaces was proposed in [Liu\&Zhang-TCOM2024]. In this work, we introduce an effective method for calculating the Hamming weight of such linear spaces using exponential sums. With this method, we derive lower bounds on the I/O cost for RS codes evaluated on a $d$-dimensional subspace of $\mathbb{F}_{q^\ell}$ with $r=2$ or $3$ parities. These bounds are exactly matched in the cases $r=2,\ell-d+1\mid\ell$ and $r=3,d=\ell$ or $\ell-d+2\mid\ell$, via the repair schemes designed in this work. We refer to schemes that achieve the lower bound as I/O-optimal repair schemes. Additionally, we characterize the optimal repair bandwidth of I/O-optimal repair schemes for full-length RS codes with two parities, and build an I/O-optimal repair scheme for full-length RS codes with three parities, achieving lower repair bandwidth than previous schemes.