System and method for improved rebuild in RAID

摘要

The present disclosure is a system and method for improved RAID rebuilds under host IO conditions, that greatly improves rebuild times and prevents host IO starvation. A queue in a drive that is part of the RAID is used to store rebuild and host IO requests, with rebuild IOs issued to the head of the drive queue. Rebuild requests in the drive are delayed by a delay time. This delay ensures there is no unintended side effect of this invention that may result in host IO starvation for the RAID system. Delay is computed as a heuristic function from a plurality of variables, such as disk head response times, time allotted for rebuild, number of rebuild threads, drive behavior, rebuild IO profile, host IO profile including workload and locality, and a timeline of sequenced events, which in one preferred embodiment cycles every 70 seconds.

主权项

1. A storage system having a plurality of drives for improved RAID rebuilds, comprising:
firmware to determine an average rebuild IO response time of a drive in the storage system; a queue internal to the drive comprising rebuild IOs and host IOs requests; firmware to delay issuance of rebuild IOs to the queue; firmware to calibrate the delay according to the parameters of average rebuild response times from the queue, a time allotted for rebuild compared to a total time and a number of rebuild threads; and firmware to issue rebuild IOs to the queue using a SCSI IO tag head-of-queue if the average rebuild response time exceeds a threshold.