Dynamical Schedule Algorithms Based on Markov Model in Tertiary Storage

摘要

Tertiary storages, such as tape libraries and optical disc libraries, are becoming the important storage devices in massive data applications. With the massive storage space they have, the tertiary storages have very low access efficiency. Designing good schedule algorithms is an important method to improve the access efficiency in tertiary storage. Stochastic Markov model is used for predicting the expected number of accesses to the data on tertiary storage. Two new schedule algorithms named MarkovMR and MarkovSRF are given also. Generally, in a tape library, there is a robot arm, a few of tape drives and a magazine where a lot of tapes located in. When the tapes are kept in tape drives, we call them online tapes. Otherwise, we call the tapes in the magazine offline tapes. Weight factors are used to above schedule algorithms to favor online tapes so that the requests for online tapes are served first before online tapes are ejected. The weighted algorithms are named wMarkovMR and wMarkovSRF. By compared to the Round-robin policy, the experimental results show that the four schedule algorithms based on Markov model have higher efficiency of data access in tertiary storage. The efficiency of wMarkovMR is highest among all the algorithms. Furthermore, the optimal factors can be derived from experiments.