R-Barrier: Rapid Barrier for Software RAID Cache Using Hints from Journaling Filesystem
Chulmin Kim, Sung Hoon Baek, Kyu Ho Park · 2012
While adopting cache in software RAID brings performance benefit, it can cause data loss at power failure which results in the broken filesystem consistency. Though I/O Barrier can be used to remove the consistency issue, it sacrifices the write performance of software RAID. To mitigate this tradeoff, we suggest R-Barrier for software RAID. The basic idea of R-Barrier is to avoid the synchronization of the entire cache space. Instead, based on given hints from the filesystem layer, R-Barrier makes software RAID cache select one of the following methods when the cache writes a certain write request into the disk: (1)Strictly ordered destaging for the write requests affecting the filesystem consistency, (2)Reordered destaging for the rest of write requests. We show that R-Barrier guarantees same filesystem consistency with I/O Barrier while the performance degradation of R-Barrier is less than that of I/O Barrier.