The RAM Enhanced Disk Cache Project (REDCAP)

This paper presents the RAM enhanced disk cache project, REDCAP, a new cache of disk blocks which reduces the read I/O time by using a small portion of the main memory. The essential ideas behind REDCAP are to enlarge the built-in cache of the disk drive, imitate its behavior, and take advantage of its read-ahead mechanism by prefetching disk blocks. REDCAP is intended to be I/O- time efficient, and implements an activation-deactivation algorithm which turns its cache on and off dynamically depending on the I/O time improvement achieved. REDCAP has been implemented in the Linux kernel. The experimental results show that our proposal reduces the application time by up to 80% for workloads which exhibit some spatial locality, while it has the same performance as a traditional system for those workloads which have a random access pattern, or perform large sequential reads.