Study On Technique Of Virtual Storage System

Virtual storage technique can extend existing data management policies to meetchanging and increasing storage requirements, it has made great progress since being putforward. Many products have been popularly used, such as easy-to use disk volumemanager, virtual tape storage, and so many kinds SAN. They provide some common virtualstorage solutions for hosts, equipments, and networking. While, it's not enough, there arestill some special issues which need more research, such as uniform management ofheterogeneous equipments, parallel I/O scheduling policies, solutions of transportbottle-neck in high-bandwidth task and serving loss of hot data, stochastic analysis of tapedrive, and so on. It is necessary to go deep into OS kernel, find ways to make virtualstorage in device driver stacks and use parallel scheduling and buffer management to getsupport for upper applications. The immediate driver locates between file system driver and HBA (host bus adapter)driver. It transforms the IRP (I/O Request Packet) from file system driver into standardformat commands. For this, OS offers corresponding class driver for storage equipments ofdifferent type. Basing on these class drivers, we put forward uniform class driver in whichall kinds of storage equipments can be recognized and managed in uniform mode. So,virtual storage pool can be constructed here. In such case, virtualization focuses on the dataorganization of storage pool and I/O scheduling mode. The former is about the managementof resources, the latter is about the transaction of IRP. Multi threads method can be used inimmediate driver, it helps make scheduling flexible, but it does not well in improving I/Operformance. Besides the immediate driver, virtual storage can be carried out in HBA driver too. InHBA driver, all peripheral equipments connected with HBA can be congregated into onestorage pool. I/O task can be distributed into multi command units to be executedconcurrently in multi I/O channels integrated on single adapter or multi adapters. So, I/Orequest packet can be transacted more quickly. I/O throughput of storage device is highlyoptimized. SPN model of parallel multi channels is constructed to analyze the parallelscheduling. It concludes that utilizing rate of I/O channels is the determinant factor forperformance improvement. In order to get higher performance in situation of small blockrequest, a buffer method is proposed. Comparing two methods mentioned above, the former doesn't need any hardware plus,it does better in offering higher reliability and availability, while the latter does better inparallel scheduling which can improve system I/O performance. The key point how to process I/O task in parallel mode lies in efficient routing andscheduling algorithms which are closely related with the environment work is done. Usingvirtual technique in immediate driver, such algorithms are studied with two real worldexamples. In the case of transport bottle-neck which may occur in high-bandwidth task, adistributed storage - parallel transport scheme is put forward. In the scheme, I/O task can bedistributed to transport in multi concurrent data links. So, I/O throughput is scaled up. Inother case of serving loss of hot data, an intelligent migration strategy is proposed. In thestrategy, hot data can be migrated automatically with the change of user requests. So,server's capability of transporting hot data changes adaptively. Active on-line storage is a developing trend of tape applications. To achieve this,medium changer is required to response more quickly in random I/O condition. Aiming atthis problem, much work has been done and some results have been concluded. While,prior solutions relied upon the structure of medium changer itself without consulting anyother aided storage. Basing on random I/O scheduling algorithms already known, a buffermanagement policy is presented. In such policy, tape library is virtualized as a block deviceand disk drive...