What is Internet Small Computer System Interface (iSCSI)
iSCSI is an acronym that stands for internet Small Computer System Interface. It is a storage area networking protocol used to send block storage from storage arrays or devices to client computers that aren’t directly connected to those devices.
An iSCSI storage area network consists of iSCSI targets on storage array controllers and iSCSI initiators on storage clients. These targets and initiators are used by the iSCSI protocol to connect storage to clients and are represented by a unique name called the iSCSI Qualified Name or IQN.
Computer operating systems include or can be installed with iSCSI clients and initiators. While some storage arrays are designed to only provide storage over iSCSI, many storage devices come equipped with iSCSI targets in addition to other common protocols.
Unlike fiber channel, iSCSI doesn’t operate over a separate network protocol. It transmits data using the TCP/IP protocol over familiar Ethernet networks that are supporting network traffic in the data center right now.
Little or no investment in new network technology is needed to start using an iSCSI SAN technology (Storage Area Network). However some deployments of iSCSI are set up with networks or subnets that are dedicated for iSCSI traffic only to maximize the bandwidth available for storage. It is also common for an iSCSI network to be deployed on fast Ethernet such as 10 Gigabit or better for this reason.
A basic Ethernet port or Host Bus Adapter is all that’s needed to connect iSCSI targets and initiators to a network. Special HBAs can be installed in computer servers that offload iSCSI transactions from the CPU to the adapter for greater efficiency or that support multiple Ethernet storage protocols such as both iSCSI and Fiber Channel over Ethernet.
Some high-speed network switches include a technology called Data Center Bridging, which makes it easier to support storage traffic and standard network traffic on the same switch ports. This is done by creating rules for quality of service. These rules define how much bandwidth each type of network traffic is allowed to consume.
In order to provision iSCSI storage an iSCSI client will typically need to be installed or activated on the client computer. The method to do this varies by operating system but is generally fairly easy. iSCSI client initiators are then added to initiator groups for iSCSI client definitions on the storage device. The name for this grouping of initiators may differ from vendor to vendor but its purpose is the same. These initiated groups are used to identify which clients may connect with storage targets.
An iSCSI LUN is created on the storage device and assigned to an initiator group or client definition at this point assuming the target and initiator are on the same IP network, the client may be able to automatically discover the target. Once the initiator is connected to the target, the iSCSI LUN at that target IQN is available for use by the client.
iSCSI LUNs are configured and used the same as any other block storage by the client operating system. The iSCSI protocol supports many features to improve security and performance.
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