X-code+: A compromised coding scheme with smaller rebuild window and load-balance

Modern storage systems call for higher reliability care beyond RAID-6 against ever-increasing data failures. And no code extension exist based on X-code, which is noted for vertical alignment and optimal update complexity. In order to construct flexible and practically reliable codes, we argue that failures happen successively and higher-level failures can be degraded into separate lower-level failures with shorter rebuilding time. Therefore, we present X-code+, a fast recoverable coding scheme by explicitly modifying and extending X-code. We modify the original X-code by redistributing elements to keep a base reliability for double-failure and further extend it with two-element tuples in one extra parity drive to shorten rebuild windows and degrade complex failure scenarios. Analysis shows that X-code+ has better recovery performance and load-balance and less update penalty than its peer codes.