This paper presents a comprehensive study on implementations and performance evaluations of two snapshot techniques: copy-on-write snapshot and redirect-on-write snapshot. We develop a simple Markov process model to analyze data block behavior and its impact on application performance, while the snapshot operation is underway at the block-level storage. We have implemented the two snapshots techniques on both Windows and Linux operating systems. Based on our analytical model and our implementation, we carry out quantitative performance evaluations and comparisons of the two snapshot techniques using IoMeter, PostMark, TPC-C, and TPC-W benchmarks. Our measurements reveal many interesting observations regarding the performance characteristics of the two snapshot techniques. Depending on the applications and different I/O workloads, the two snapshot techniques perform quite differently. In general, copy-on-write performs well on read-intensive applications, while redirect-on-write performs well on writeintensive applications.

The system architecture cannot adapt to the dynamic change of system disks, which is a general problem in traditional storage system. While EvoRAID system, a dynamic storage system we proposed, applies DAA algorithm to cope with three kinds of storage system disk changes - homogeneous disk adding, heterogeneous disk adding, and heterogeneous disk replacement. Simulation results demonstrate that without stopping system I/O service, EvoRAID system can assimilate the adding/replacing homogeneous/heterogeneous disks gradually with little extra system overhead, and achieve optimized storage capacity and I/O performance.