The iSCSI protocol is a transport for SCSI over TCP/IP. Until recently, the standard IP protocol infrastructure (i.e., Ethernet) could not provide the necessary high bandwidth and low latency needed for storage access. A special communications infrastructure, mainly Fibre Channel running FCP (SCSI over Fibre Channel), was developed to allow Storage Area Networks (SANs). With the recent advances in Ethernet technology, it is now practical (from a performance perspective) to access storage devices over an IP network. 1 Gigabit Ethernet is now widely available, and is competitive with 1 and 2 Gigabit Fibre Channel. Soon 10 Gigabit Ethernet will also be available. Similar to FCP, iSCSI allows storage to be accessed over a Storage Area Network, allowing shared access to storage. A major advantage of iSCSI over FCP is that iSCSI can run over standard, off-the-shelf network components, such as Ethernet. A network that incorporates iSCSI SANs need use only a single kind of network infrastructure (Ethernet) for both data and storage traffic, whereas use of FCP requires a separate type of infrastructure (Fibre Channel) and administration for the storage. Furthermore, iSCSI (TCP)-based SANs can extend over arbitrary distances, and are not subject to distance limitations that currently limit FCP.
Since iSCSI is designed to run on an IP network, it can take advantage of existing features and tools that were already developed for IP networks. The very use of TCP utilizes TCP's features of guaranteed in-order delivery of data and congestion control. IPSec can be leveraged to provide security of an iSCSI SAN, whereas a new security mechanism would have to be developed for Fibre Channel. SLP (Service Location Protocol) can be used by iSCSI to discover iSCSI entities on the network. Thus, in addition to iSCSI running on standard, cheaper, off-the-shelf hardware, iSCSI also benefits from using existing, standard IP-based tools and services.