ROE: Repair-Oriented Encoding for Erasure Codes with Localities

Abstract

Modern storage systems replicate new data for fast access and later encode aged data into erasure coding for storage efficiency. However, the encoding process incurs substantial cross-rack traffic and affects the future repair cost. Existing approaches compromise either post-encoding repair efficiency or on-encoding performance due to overlooking the characteristics of the erasure-coded layout. We propose Repair-Oriented Encoding (ROE), a scheme for erasure codes with localities that jointly minimizes the on-encoding cross-rack traffic and post-encoding repair cost. ROE targets the repair-optimal coding layout to reduce future repair cost and proactively aligns the replication layout to match the coding layout. It further exploits localities to offload the computation of local parity blocks to their destination racks, often eliminating the on-encoding traffic entirely. Experiments show that ROE reduces the encoding time by up to 97.8% and post-encoding repair time by up to 94.7%, while maintaining comparable replication read/write performance.