The Research On Remote Boot ISCSI Virtual Storage Host Channel

As the information resource is growing rapidly, computing model developes into the model of storage separated from computation. The concept of network computing is in accordance with the demand of separating storage from computation. Storage will become the center of IT technology in future. The iSCSI (internet SCSI) protocol combines the advantage of SCSI and TCP/IP protocol, so it is the first choice for network storage.Remote boot iSCSI virtual storage host channel is designed for client host, which remotely boots from storage server in iSCSI network computing system. This paper investigates policies of remote boot and I/O redirection and technology of I/O acceleration for client hosts based on iSCSI protocol.The following are the main task of research in iSCSI virtual storage host channel. At first, it reads content of ISDH (iSCSI Session Data Header) from BIOS shadow memory, which includes local IP address and iSCSI session login parameters. In this way, OS can change working mode from real mode of processor to protected mode.Secondly, it provides service of I/O redirection for OS via mapped virtual SCSI HBA (Host Bus Adapter) and virtual SCSI disk while OS is working in protected mode. The task of transformation between SCSI CDB (Command Descriptor Block) and iSCSI PDU (Protocol Data Unit) is completed by TDI (Transparent Driver Interface) client program.At last, it introduces I/O acceleration for iSCSI virtual storage host channel: iTRM (iSCSI Transparent Reliable Multicast) protocol. The iTRM protocol introduces reliable multicast protocol into iSCSI session, and patches up weakness of TCP unicast transparent model in iSCSI session. The iTRM protocol expands the definition of iSCSI PDU, so that iSCSI session can comprehend iSCSI multicast session announcement. The iTRM protocol investigates the launch policy of multicast session, which is executed by multicast monitor agent. The retransmission of lost data for multicast session is transmitted via iSCSI session, so that the reliability of multicast session is guaranteed.Test results show that the iSCSI virtual storage host channel can make OS remotely boot from storage server, and the speed of booting is equal to PC that booting from local IDE disk. Test results also prove that the function of virtual SCSI disk is alike to real disk, and the I/O throughput of virtual SCSI disk is not less than local IDE disk. When there are several client hosts booting simultaneously, the iTRM protocol improves booting speed of OS and loading speed of applications for client hosts.