The Design And Implementation Of Virtual Disk Based On ISCSI Protocol

In the hierarchical storage system based on iSCSI protocol, multiple requests ofstorage resources from the client will create multiple logical volumes in the host computer,and the continued migration of hot data will also produce more and more fragmentation.All these will increase the difficulty of system management, and the reliability of thesystem will decrease as well. Most of the existing virtual device management methods usethe strategy of resource reservation and static allocation, but they all have a low utilizationof storage devices. In order to meet the requirement of the hierarchical storage systembased on iSCSI protocol and achieve the thin provisioning of storage resources, we mustdevelop a new virtual disk controller.The virtual disk controller is realized by a virtual block device mapping module inthe block device driver layer, all logical volumes are organized into a single logicalstorage unit which is available to the file system as a simple disk and can manage thefragmentation caused by data migration. The virtual disk controller uses dynamic addressmapping strategy to manage the mapping relationship between the virtual device and thephysical devices which are connected to local host by iSCSI protocol. The controllerallocates physical storage resources for the virtual device only when actual requests occur,so as to achieve the purpose of thin provisioning. In consideration of the fact that thevirtual disk controller needs to fetch the mapping table ietms frequently when the read andwrite requests are redirected, the controller adopts the B-tree algorithm to improve the rateof searching process. The virtual device mapping module provides a scheduling layer tothe cache and merge the adjacent read and write operations which are redirected on thesame physical device, which can improve the virtual disk throughput at random accessmode.The prototype system based on iSCSI protocol has been realized, and the tests showthat the virtual disk controller achieves the purpose of unified management of logicalvolumes and dynamic allocation of storage resources. The results also show that thesequential access mode performance of the virtual disk almost has not been effected, thethroughput of the local virtual disk is increased by9%and the throughput of the network virtual disk is reduced by11%at random access mode. Therefore, the virtual diskcontroller can provide the desired functions under the premise of parttally minor sacrificeof system performance.