IP-based storage: Benefits and challenges

Posted on March 01, 2001

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Block-level IP storage promises numerous advantages, but there are still many hurdles to overcome.

BY RON LEVINE

Storage area networks (SANs), SAN/WAN connectivity, and Internet Protocol (IP)-based storage networks are key technologies that promise to expand the boundaries of traditional data storage. The latest push is to use the IP infrastructure for both network and storage traffic, which has resulted in the emergence of block-level (as opposed to file-level) IP-based storage networking, a concept that will use protocols such as iSCSI to connect storage devices to traditional IP networks. IP-based storage has materialized as a result of the desire for standardization of networking protocols. Although still in its infancy, IP-based storage would provide a broader range of interface options for SAN implementations.

Expected benefits

IP-based storage is evolving quickly and is expected to offer benefits ranging from improvements in throughput rates to complete interoperability between storage components. With IP-based storage, SANs will use standard IP networks such as Gigabit Ethernet. Ethernet-based LANs have long been the industry standard, and the idea of creating a SAN with Ethernet holds great appeal for many IT organizations. Some of the potential advantages of IP-based storage networking include

  • Labor and equipment costs for connectivity and management will be reduced because IP and Ethernet exist in most shops today.
  • Overall performance should improve because Ethernet speeds are expected to increase at a much faster rate than Fibre Channel.
  • There are no distance limitations with IP, and SAN/LAN/WAN connectivity is supported. IP-based storage paves the way for remote backup and recovery over long distances, which is ideal for business continuity and disaster recovery.
  • Recent connectivity improvements between Fibre Channel and IP switches should eliminate interoperability issues and improve WAN connectivity.
  • A Fibre Channel SAN employing IP for LAN/MAN/WAN connectivity will not have any distance limitations.

From an operational standpoint, the cost savings are likely to be significant. "Because Ethernet is common in most environments, and companies already have expertise and comfort managing Ethernet networks, the need to train staff on a new technology and purchase additional management tools is eliminated," says Tim Rasmussen, senior product manager at Datalink, an independent integrator that specializes in storage.

The iSCSI protocol is a standard being developed by the Internet Engineering Task Force (IETF) to map the SCSI protocol over TCP/IP. This approach will enable storage devices to be attached to IP-based networks. The iSCSI standard will leverage the Transmission Control Protocol (TCP) because of its industry-wide acceptance, reliability, and defined standards.

At the LAN/SAN level, TCP will provide fault detection and recovery, and at the LAN/WAN level, TCP end-to-end connectivity should minimize traffic congestion, improve the reliability of data transfers, and eliminate the need for protocol conversion equipment. iSCSI will enable end users to link SANs to LANs, MANs, and WANs using the standard IP protocol.

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Although the iSCSI standard is not expected to be finalized until at least year-end, a number of "pre-iSCSI" solutions are already emerging. For example, Nishan Systems' Storage over IP (SoIP) is an umbrella term for a set of IP-based storage products. SoIP, which Nishan says will be compatible with iSCSI when the standard is completed, enables a variety of interfaces-including Fibre Channel and SCSI-to connect to traditional IP-Ethernet networks. SoIP is expected to blend the high-speed, highly available Fibre Channel SAN architecture with the reliability and compatibility benefits of the IP network to create a single network and storage infrastructure. (For more in-formation on Nishan's SoIP products, see p. 1).

IP storage limitations

However, it's important to point out the limitations of IP-based storage. Currently, no standards have been completed. Also, the TCP/IP protocol stack is very CPU-intensive, although future hardware and component developments may help to overcome this limitation. Substantial development must occur for network interface cards (NICs) to handle IP-iSCSI traffic with adequate performance for storage applications. Without NICs with hardware accelerators, the only practical application for iSCSI is to extend current Fibre Channel SAN-to-LAN connectivity into the realm of SAN-to-MAN/WAN connectivity.

Evolution of IP-based storage

"First-generation IP-based storage networking solutions will include Fibre Channel tunneling and SCSI encapsulation products," according to Datalink's Rasmussen. "Fibre Channel tunneling, used for connecting SAN islands, encapsulates Fibre Channel control codes and data into IP packets and transfers them to a remote Fibre Channel SAN across a WAN. SCSI encapsulation products, on the other hand, support direct block-level data transfers from a host to a storage device using a standard NIC connected to an Ethernet network." Specialized Ether-net NICs similar to today's Fibre Channel and SCSI host adapters are being developed to handle SCSI tasks.

Preparing for widespread adoption of IP-based storage networking, storage device manufacturers are working on a variety of next-generation products. In the switch arena, Nishan has developed SoIP switches that support Gigabit Ethernet, SCSI, and Fibre Channel. Nishan is also expected to introduce SoIP adapter cards later this year.

Storage switches should improve drastically in the near term as vendors resolve interoperability issues in support of the SAN/WAN infrastructure. For example, Brocade Communications and Cisco Systems are co-developing a switch based on Cisco's Catalyst 6000 IP switch that will incorporate a Fibre Channel blade, allowing IP and Fibre Channel connectivity. This endeavor will enable Fibre Channel SANs to connect to IP-based MANs and WANs across much longer distances than is possible with Fibre Channel, which is limited to 10km (about 6.2 miles).

Other storage components are also evolving. For example, via its acquisition of NuSpeed last year, Cisco has designed a SCSI-over-IP device that works as an intermediary component that provides a gateway to the SAN. This device will allow storage on a SAN to be connected to an IP network.

The move to create protocols and products that will use existing IP-based networks to connect SANs to LANs, MANs, and WANs is a natural progression that will change the way data is accessed, stored, and protected. "If successful, organizations won't be limited to Fibre Channel as the only underlying technology to build a SAN," says Data-link's Rasmussen. "In the future, existing network infrastructures may be leveraged to create an Ethernet-based SAN; SCSI encapsulation technology may provide the option of creating a network and storage architecture based solely on IP over a WAN."

Meanwhile, Fibre Channel remains the only practical method of building a large-scale, reliable, and high-availability SAN. When it arrives, IP-based storage networking will expand the data storage boundaries, creating a much more flexible data management architecture.

Ron Levine is a freelance writer in Carpenteria, CA.


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