Implementation and Performance Evaluation of Two Snapshot Methods on iSCSI Target Storages

While snapshots have been commonly used in data storages for backup and data protections, little is known in the open literature how such snapshots impact application performance. This paper presents an implementation and performance evaluation of two snapshot techniques: copy-on-write snapshot and redirect-on-write snapshot. Our implementation is carried out at block level on a standard iSCSI target. We carry out quantitative performance evaluations and comparisons of the two snapshot implementations using TPC-C, TPC-W, IoMeter, and PostMark 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 write-intensive