CoRD: Combining Raid and Delta for Fast Partial Updates in Erasure-Coded Storage Clusters

A significant drawback of erasure-coding is suffering from the expensive update traffic. The analysis of real-world-production traces shows that partial updates, including partial-block-updates and partial-stripe-updates, are both common. Existing schemes cannot work adequately for partial updates. Raid-based scheme coordinates multiple updated entire blocks to update parity, yet it incurs significant network traffic for partial-block-updates. Delta-based scheme transmits the updated parts and independently updates parity, yet it cannot share computed-delta parts for partial-stripe-updates. We propose CoRD, which optimally combines Raid-based and Delta-based schemes to minimize the update traffic. It exploits the offset address intersections between multiple updated blocks and only transmits the updated parts to coordinate in parity updates. CoRD further address cross-block update scenarios by flipping some dedicated blocks to improve the performance. Comprehensive evaluations verify the effectiveness of CoRD for the latest traces, with the update traffic reduction of 37.02%-87.19% and the performance improvement of 36.54%-231.92% compared to state-of-the-art.