Abstract: Storage virtualization can enhance the overall quality of service in storage are a networks. Out-of-band virtualization, in contrast with in-band virtualization, has the advantages of high performance and good scalability. In this paper, a policy for guaranteeing the persistent consistency of virtualization metadata is proposed, which enables out-of-band virtualization to survive panics and power failures by means of ordered operations in a virtualization transaction, REDO logging and log integrity checking. An organizing mode of the on-disk virtualization metadata is described, which is human-readable and easy to modify due to the introduction of a relation model. An effective approach which obtains the volume layout by analyzing the partition tables on legacy disks is presented for integrating typical legacy storage systems, and little time is needed to upgrade large legacy systems by the approach. The implemented prototype based on these key technologies demonstrates its ability to provide high performance in the representative experiments.