A Hybrid Storage System Composed of On-the-Fly Automated Storage Tiering (OTF-AST) and Caching

In a previous workload study, we found a new type of I/O concentration approximately 6 GB in size that continues for more than 10 minutes and then moves on to another area. We also found that the conventional hybrid storage method, static tiering and caching, is not sufficient for this I/O concentration. The on-the-fly automated storage tiering (OTF-AST) designed for this I/O concentration cannot handle other I/O concentrations well, so we have developed a hybrid storage system composed of both OTF-AST and caching. In the proposed system, the OTF-AST dynamically migrates the new I/O concentration to SSD and the caching handles the other I/O concentrations. Experimental results showed that the hybrid storage system surpasses the basic OTF-AST system with an average response time 27% better for one of a typical samba workload in which read is not predominant and I/O concentration lasts for 20 minutes.