Storage over IP awaits enhancements

Enterprisewide storage implies connecting users to storage resources over a WAN. Historically this has been accomplished using relatively expensive dedicated circuits. New developments in storage network technology are enabling transparent storage connectivity over standard IP networks.

Storage over IP should take advantage of an organization's existing or planned IP backbone to move storage data without intersecting LAN traffic. Further, data over IP should provide connectivity and conversion among servers and storage devices, or between storage devices that use drive interface protocols such as SCSI and Fibre Channel. (Editor's note: A different perspective on storage over IP will be presented in a future Technology Update.)

A multigigabit switching platform can extend storage networks, including Fibre Channel storage-area networks (SAN), over WANs by integrating channel technology, high-speed network technology, and open systems hardware and software into one platform. This switching platform can operate over a routed, virtual or private IP network.

The switching platform will perform IP encapsulation/decapsulation, which converts data packets to IP packets in preparation for travel over the IP network. Further, it can perform load balancing and create alternate paths over multiple IP interfaces or transport circuits, which provides powerful network management capabilities available on dedicated links, without the cost.

How it's done

Creating a way to move stored data over an IP network requires that a viaduct between the storage resources and the IP network be established. A viaduct is a device that manages connections for data transfer between storage devices, using an IP network for transport. A viaduct will convert data frames to IP packets.

Additionally, a viaduct will convert received IP packets into data frames for remote storage, backup or mirroring.

IP operates at the network layer, Layer 3 of the Open Systems Interconnection stack. The IP layer analyzes the addresses in packet headers and routes packets across subnetworks. The transport layer (Layer 4) ensures reliable transport of packages being sent. Standard TCP was not designed for large-block I/O used in volume data transfers. Therefore, storage over IP, which will typically deal with large amounts of storage data, must be enhanced with built-in transport abilities at Layer 4.

To create a premium class of service that will be suitable for low latency applications such as data mirroring, it is necessary to improve the functionality of Layer 4. This can be accomplished by creating a new transport layer similar to TCP but enhanced for storage that replaces or enhances the TCP layer, making data transmissions faster and more efficient. The viaduct will manage the details of this new layer.

Working within IP presents problems other than lack of interoperability and higher latency. Key technical issues must be solved before storage networking and storage data services can be broadly deployed over private or public IP networks. These issues include quality of sevice, dropped packets, security and network management.

Larsen is director of product management - open systems at Computer Network Technology. He can be reached at brian_larsen@cnt.com .