Extending SANs through FCIP

Fibre channel over Internet protocol (FCIP) will play a key role in IP-SAN (IP storage area network) strategies in the near future, as it extends the ability of fibre technology to enable support for data replication over WAN (wide area network).

Speaking at a Hewlett-Packard Co. storage event last week, Roger Archibald, vice president of Infrastructure and NAS (network attached storage), HP Network Storage, said, value-added protocols such as FCIP will integrate seamlessly and transparently to create a global storage network. FCIP extends the reach of FC, which has a physical limit of 100 kilometres, by utilizing IP routing technology.

He believes that with the aggressive and mature road map for FC, the technology will remain as the springboard for SAN-wide deployment for storage virtualization.

FCIP is an IP-based storage networking technology developed by the Internet Engineering Task Force (IETF). FCIP mechanisms enable the transmission of FC information by tunnelling data between SAN facilities over IP networks. They do this by translating FC control codes and data into IP packets for transmission. This facilitates data sharing over a geographically distributed enterprise.

Archibald believes that the alternative approach to storage data transmission over IP networks, iSCSI (Internet small computer system interface), will play a restricted role as part of the NAS environment, remaining as a low cost storage at the network edge or working as a bridge onto FC, said Archibald.

SCSI is an intelligent protocol that enables data blocks to be read from or sent at high speed to a storage device such as a disk or tape drive. ISCSI, which was also developed by the IETF, is the new IP-based storage networking standard for linking data storage facilities. By carrying SCSI commands over IP networks, iSCSI is used to facilitate data transfer over intranets and to manage storage over long distances.

Like FCIP, the iSCSI protocol is among the key technologies expected to help bring about rapid development of the SAN market, by increasing the capabilities and performance of storage data transmission. Because of the common usage of IP networks, iSCSI can be used to transmit data over LANs (local area networks), WANs or the Internet and can enable location-independent data storage and retrieval.

When an end user or application sends a request, the operating system generates the appropriate SCSI commands and data request, which then go through encapsulation and, if necessary, encryption procedures. A packet header is added before the resulting IP packets are transmitted over an Ethernet connection. When a packet is received, it will be decrypted if it was encrypted before transmission and disassembled, separating the SCSI commands and request. The SCSI commands are sent on to the SCSI controller, and from there to the SCSI storage device. Because iSCSI is bidirectional, the protocol can also be used to return data in response to the original request.

iSCSI can run over existing Ethernet networks while FCIP can only be used in conjunction with FC technology; in comparison.

SAN connectivity, through methods such as FCIP and iSCSI, offers benefits over the traditional point-to-point connections of earlier data storage systems, such as higher performance, availability, and fault-tolerance.

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