The host interfaces of iSCSI devices are generally IP interfaces by default, and can be directly connected to Ethernet switches and iSCSI switches to form a storage area network. There are three connection methods between the iSCSI device and the host, depending on the host-side HBA card and network switch. The first type: Ethernet card + initiator software. Hosts such as servers and workstations use standard Ethernet cards and are directly connected to Ethernet switches through Ethernet cables. ISCSI storage is also connected to Ethernet switches through Ethernet cables or directly to the Ethernet cards of hosts. Install the initiator software on the host. After the Initiator software is installed, the Initiator software can virtualize the Ethernet card as an iSCSI card, and receive and send iSCSI data packets, thereby realizing the transmission function of the iSCSI protocol and the TCP / IP protocol between the host and the iSCSI device. This method uses ordinary standard Ethernet cards and Ethernet switches without additional adapters, so the hardware cost is the lowest. The disadvantage is that some of the resources on the host side are the main points for the conversion of ISCSI packets and TCP / IP packets. But in the application environment with low I / O and low bandwidth performance requirements and fully meet the data access requirements. At present, many of the latest versions of common operating systems provide free initiator software. Building a storage system, except for the storage device itself, basically does not need to invest more money, so the construction cost is the lowest among the three system connection methods . The second type: hardware TOE network card + initiator software mode. The first method uses ordinary Ethernet cards and Ethernet switches without additional configuration adapters or dedicated network equipment, so the hardware cost is the lowest. However, the packaging and unpacking of ISCSI packets and TCP / IP packets all require the host main processor CPU to perform calculations. The data transmission rate is directly affected and limited by the host ’s current operating state and available resources, so it generally cannot provide high bandwidth. And high IOPS performance. The intelligent Ethernet card with TOE (TCP Offload Engine) function can transfer the processing of network data traffic to the integrated hardware on the network card to free the system main processor CPU from the heavy kernel interrupt service busy with protocol processing , The host only undertakes the task of processing TCP / IP control information. Compared with the first method, the TOE card can greatly increase the data transmission rate. The function of the TCP / IP protocol stack is performed by the TOE card, while the function of the iSCSI layer is still performed by the host. Since the TOE card also uses TCP / IP protocol, which is equivalent to a high-performance Ethernet card, the second method can also be regarded as a special case of the first connection method. The third type: iSCSI HBA card connection. Install a professional iSCSI HBA adapter card on the host to achieve efficient data exchange between the host and the switch, and between the host and the storage. Compared with the first two methods, the third connection method uses an iSCSI HBA card, so the data transmission performance is the best and the price is the highest. Both of the latter two methods require special hardware boards to be installed on the host, because the current market prices of TOE network cards and iSCSI HBAs are relatively expensive. If there are many hosts in the network, the total network investment may not be much lower than that of FC-SAN storage system, but the bandwidth and performance of the network are much worse than FC-SAN storage system. Some people may ask, why aren't iSCSI switches adopted in these three ways? In fact, the iSCSI switches we can see on the market are not switches in the true sense. The so-called iSCSI switches should be called iSCSI protocol converters, or iSCSI bridges. One part of the port is used to connect the host's iSCSI HBA card, and the other part is used to connect the FC storage or SCSI storage. It can only achieve the FC-iSCSI (or SCSI-iSCSI) protocol connection between the storage device and the host, but cannot implement iSCSI-iSCSI. Protocol connection, its working mode is completely different from that of Ethernet switch or FC switch, to achieve interconnection and interworking within a certain protocol. Therefore, iSCSI switches are generally used as controllers in iSCSI storage, rather than network connection devices between iSCSI storage and hosts. 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iSCSI storage connection