Erasure-Coded Multi-Block Updates Based on Hybrid Writes and Common XORs First

Abstract

Erasure code is widely used in storage systems since it can offer higher reliability at lower redundancy than data replication. However, erasure coding based storage systems have to perform multi-block updates for partial writes of an erasure coding group, which leads to a large number of XOR operations. This paper presents an efficient approach, named ECMU, for erasure-coded multi-block update under a stringent latency by scheduling update sequences. ECMU takes a hybrid of reconstructed-write and read-modify-write for parity blocks of an erasure coding group, it dynamically selects the write scheme with the fewer XORs for each parity block to be updated, in order to reduce the number of XORs. ECMU iteratively retrieves the unmodified parity blocks to calculate the minimum XORs for each write scheme. For all parity blocks to be updated, after the write schemes are determined, ECMU performs the common XORs first, then it reuses the computational results to further reduce the number of XORs. ECMU caches a certain number of scheduling schemes to reduce the construction count of the scheduling schemes. Experimental results on real-world trace replaying show that the number of XORs and update time can be reduced significantly, compared with the state-of-the-art.