The Design and Implementation of RAPID-Cache: A Reliable, Inexpensive, and High-Performance I/O Cache for Linux

Most file system performance enhancing techniques, such as the I/O buffer cache and the Log-structured File Systems (LFS), re-lying on caching data in volatile RAM for a period of time be-fore destaging them to disk. Such approaches pose a reliability problem. Non-volatile RAM (NVRAM) caches can be used to enhance the reliability. However, large NVRAM caches are very expensive and not as reliable as disks. This paper presents the design and implementation of a dif-ferent approach called RAPID-Cache (Redundant, Asymmetri-cally Parallel and Inexpensive Disk Cache) for highly-reliable systems. The new approach provides an inexpensive way to make the OS buffer cache non-volatile and highly reliable. Re-cent researches using simulation suggest that as a cache inside a disk array controller, RAPID-Cache has great reliability/cost advantages over conventional write cache structures. In order to validate whether RAPID-Cache can really achieve satisfac-tory performance in real systems, and to see if RAPID-Cache can also improve the performance/reliability of the OS buffer cache, we have designed and implemented RAPID-Cache for the Linux system. Measurement results using realistic benchmarks show very promising results. Using only 3.25 MB of NVRAM, a RAPID-Cache outperforms normal NVRAM caches of 64 MB or even 128 MB. RAPID-Cache also provide better reliability than normal NVRAM caches.