With Ethernet reaching Gigabit and even 10 Gigabit speeds, and the current move to network-based storage, it was inevitable for the industry to explore ways to utilize Ethernet as a storage network technology.
That’s the basis for iSCSI. The payoff is simple: With iSCSI there isn’t a requirement to learn how to set up and manage two different (storage and data) technologies. IT managers can still use Fibre Channel, but only as it was originally conceived, as a storage device interface.
iSCSI enables universal access to storage devices and storage-area networks over standard Ethernet-based TCP/IP networks. These networks may be dedicated or shared with traditional Ethernet applications. IP routers and switches can be used to extend the IP storage network to the wide area for applications such as synchronous and asynchronous remote disk copy, or tape backup and restore.
In the WAN, TCP will ensure data reliability, manage network congestion and adapt retransmission strategies to WAN delays.
As with the standard SCSI protocol, iSCSI requires an initiator and a target. Therefore, for iSCSI to work as a transport system, it requires iSCSI drivers installed in servers to initiate iSCSI packets, by which block-oriented SCSI data is encapsulated into an iSCSI wrapper. This packet is then routed across IP networks and ultimately sent to an iSCSI target device, which converts the embedded SCSI data to Fibre Channel.
Management and security features, including logical unit number mapping and access control lists, ensure data integrity throughout this process, making sure servers store and retrieve information from the targeted storage devices according to configurations defined by a network administrator.
One of the key requirements for high-performance iSCSI networking is for operation without consuming more host CPU cycles than SCSI or Fibre Channel. Understanding this requirement, leading network interface card (NIC) and host bus adapter vendors are developing iSCSI-based products with TCP acceleration features. Soon, most servers will be able to use an iSCSI-specific NIC that will contain a TCP offload engine that reduces the load on the CPU. The net result will be iSCSI storage networks that are as efficient as directly attached Fibre Channel or SCSI storage.
Enterprise Applications
iSCSI lets companies connect more servers to each other in high-performance corporate storage networks over greater distances. This gives IT managers more flexibility in designing and applying enterprise storage networks. Examples of typical iSCSI-based applications we can expect corporations to run are: