A-Cache: Asymmetric Buffer Cache for RAID-10 Systems Under a Single-Disk Failure to Significantly Boost Availability

The RAID-10 architecture has been widely deployed in commercial and industrial storage environments over the past two decades due to its high reliability, availability, and performance. However, during the recovery process of a single disk failure, which accounts for more than 99.75% of the disk failure scenarios, it is still at a high risk of data loss and suffers from a degradation of user I/O performance, which results from the severe interference between the user and recovery I/Os. Based on our observations and analyses, we find highly asymmetric disk bandwidth utilization and disk I/O interference during the recovery process of the RAID-10 systems under the single faulty-disk condition. Motivated by the fact that this asymmetry can be leveraged to significantly and simultaneously speed up the recovery and user I/O performances. As a result, we propose a novel asymmetric buffer cache management scheme, called A-Cache, to mitigate this asymmetry by allocating cache space asymmetrically between the disks that do not participate in the recovery process and those that do. To verify the effectiveness of the A-cache, we have integrated A-Cache into the popular cache algorithms LRU, named A-LRU. The evaluation of our prototype system demonstrates that A-LRU is able to significantly speed up the recovery speed and average user I/O latency under various typical configurations, compared to the original LRU, without any additional hardware cost.