R-Barrier: Rapid Barrier for Software RAID Cache Using Hints From Journaling Filesystem

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Executive Summary

While adopting cache in software RAID brings performance benefit, it can cause data loss at power failure which results in the broken file-system 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, the authors 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 file-system layer, R-Barrier makes software RAID cache select one of the following methods when the cache writes a certain write request into the disk: strictly ordered destaging for the write requests affecting the file-system consistency; reordered destaging for the rest of write requests.

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