Building iSCSI storage area networks.

Although the price of storage hardware has been steadily decreasing, the voracious demand for data (on average, capacity requirements double every 16 months) and the associated administrative and maintenance costs continue to strain budgets and staff. Organizations that primarily use direct-attached storage (DAS) find it especially challenging to manage and scale these storage systems in an efficient and cost-effective manner.

One way of surmounting this challenge is to consolidate storage into a storage area network (SAN), which centralizes storage resources and reduces points of management. Not only does a SAN facilitate scaling and enhance availability, it makes it possible for disparate platforms and applications to share the same storage environment, greatly improving utilization, efficiency, and storage administrator productivity.

Until recently, Fibre Channel (FC) has been the sole means of implementing a SAN. However, FC comes with a significant price tag and often requires capital and resource investments in complicated and proprietary technologies. For applications deemed mission critical, large businesses have been able to justify the high cost of owning Fibre Channel SANs. For many applications like e-mail and databases, FC SANs remains prohibitively expensive in terms of cost and complexity.

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To be viable for a broad range of environments and applications, first and foremost, networked storage must be affordable and easy to install, manage and scale. Support for industry standards is vital to ensuring interoperability across different platforms.

Today, the iSCSI protocol makes it possible to extend the benefits of consolidated storage throughout the industry. Devised by the Internet Engineering Task Force--the same organization that created the TCP/IP standard--the iSCSI protocol lets businesses leverage existing IP skills and infrastructure to create Ethernet-based SANs that deliver the features and performance of Fibre Channel, but at a fraction of the cost and greater simplicity.

How iSCSI Works

The iSCSI protocol is built on SCSI and Ethernet, the dominant industry standards for storage and networking. Utilizing an ordinary IP network, iSCSI transports blocklevel data between an iSCSI initiator on a server and an iSCSI target on a storage device. Authentication methods are used to provide security between initiator and target.

When an iSCSI initiator connects to an iSCSI target, the storage is seen by the server operating system as a local SCSI device that can be formatted as usual. The underlying storage is transparent to applications and operating systems (see Figure 1).

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To access storage in an iSCSI SAN, a server needs only an iSCSI initiator connected to an IP network. An initiator can be an iSCSI driver with a standard network card or a card with a TCP offload engine (TOE), which reduces CPU utilization. Also available are host bus adaptors (HBAs) that offload both TCP and iSCSI.

Interoperability across operating systems, applications and hardware is a key benefit of an iSCSI SAN. By providing access to storage at the block level, iSCSI lets heterogeneous servers and applications share the same storage resources. This capability is analogous to the interaction between Web servers and browsers--devices that work together, regardless of platform.

Using a Gigabit Ethernet network, an iSCSI SAN delivers performance comparable to Fibre Channel. Ethernet's long history of improvement, including recent advances in 10Gb Ethernet, ensures the long-term performance viability of iSCSI and graceful network upgrades. Technologies such as multi-path I/O can also be used to improve availability and increase bandwidth.

Despite its recent appearance in the storage world, the iSCSI protocol is widely accepted in the industry and supported by all the major operating systems, including Windows, Linux, Novell and Solaris. Today, many prominent storage vendors are delivering products based on the iSCSI protocol, including Adaptec, Cisco, Intel, QLogic, and a number of innovative emerging companies.

Common Myths About iSCSI

In reviewing the capabilities of iSCSI, it is important to understand that iSCSI does not:

* Change how an operating system works or perceives storage. Once an iSCSI initiator connects to an iSCSI target, the device appears on the server as a regular SCSI disk.

* Require high overhead on the host. iSCSI's broad connectivity options allows for choice in the host connection to storage. This flexibility allows administrators to choose the most cost- effective connection, and the easy ability to change connection method as needed.

* Modify how storage devices work. Using iSCSI does not affect the features, performance, expansion, or price of storage arrays.

* Alter the cost of storage devices. Implementations of iSCSI storage arrays, like any other storage device, can be cheap or expensive, feature-poor or feature-rich.

Comparing SAN Cost Factors

What has prevented the widespread use of SANs to date is the cost and complexity of deploying and maintaining the environment. Administrators must install and manage many individual hardware and software components, some of which may not work in a heterogeneous environment or may require significant customization. The burden of supporting and upgrading disparate elements is beyond the means of many organizations.

Whether based on iSCSI or Fibre Channel, every SAN includes the following key components:

* Hosts that use the storage

* Initiators that perform SCSI operations on the host

* Storage devices

* Network switches that handle I/O traffic between initiators and storage devices

The difference lies in the technology incorporated within the components. In an iSCSI SAN, these components are based on standard Ethernet: cards, switches, and interfaces, all relatively inexpensive hardware components.

iSCSI SANs offer a great deal of flexibility in initiator deployment options. Initiators can be iSCSI drivers that utilize Ethernet cards or iSCSI HBAs. With software-based iSCSI initiators, businesses can achieve host connectivity to a SAN in an easy and affordable manner. In the future, hosts will have TOEs on the server motherboard, completely offloading CPU processing without additional hardware.

In addition, high volumes of Ethernet switches and network cards along with fierce industry competition ensure low-cost iSCSI connectivity--now and in the future.

Component Fibre Channel iSCSI Average Savings Host Initiator $ 800-$1800 $ 0-$600 77% Switch Ports $ 400-$1800 $ 25-$800 63% Total Cost $1200-$3600 $25-$ 1400 70% Table 1: Per-connection costs of iSCSI as compared to Fibre Channel

Another important cost factor is management costs. Unlike an Fibre Channel SAN, which often requires specialized staffing and training, all administrators understand TCP/IP setup and operation. iSCSI interoperates seamlessly, avoiding the interoperability issues that continue to plague FC SANs. This results in easy deployments, operation and upgrades.

But a SAN cannot sacrifice features for affordability. Whether a SAN provides storage to mission critical applications or departmental applications, it must deliver high availability, hot swappable hardware, snapshot capabilities, disaster tolerance, and intuitive user interfaces. Not only is iSCSI capable of providing this functionality, it makes it possible to design a consolidated storage solution that simplifies the entire range of management operations, including backup and restore operations, load balancing, and provisioning--utilizing a network infrastructure that is familiar to IT personnel.

The Impact of iSCSI and the Future of SANs

The benefit of using iSCSI as a transport mechanism for connecting servers to storage is increasingly apparent. Still, the question remains: What does iSCSI do to make networked storage more accessible to a broad range of businesses, especially those who are looking to consolidate their direct attached environments?

One school of thought believes that the way SANs currently work is adequate, and iSCSI is "just another wire" for connecting hosts to storage. These folks argue that SANs should continue to operate and evolve much as they have in the past.

Others believe that the way SANs work today is not acceptable and see iSCSI as a catalyst for innovation. The large, potential market for a low-cost, easy-to-deploy SAN fuels the belief that iSCSI will invigorate advances in storage designs and ease of use.

By using iSCSI, not only is the network portion of a SAN greatly simplified, but the costs of hardware, staffing, and software management tools are reduced. The standards-based iSCSI protocol makes interoperability truly possible and eases the burden of upgrades. These benefits allow storage to be consolidated in both large and small datacenters. With an iSCSI SAN, installation and operation are no longer restricted to highly skilled individuals, but open to any administrator with a modicum of network experience.

History will show whether iSCSI will lift storage technology to new heights of innovation. Given the fierce competition in the industry, most observers agree that the advances seen in other areas of computing (including virtualization and automated operation) will soon be incorporated into the world of storage area networks.

With its inherent cost-effectiveness and strong industry backing, the future is bright for iSCSI as the foundation for a robust, consolidated storage solution for all enterprises.

Table 1

Component        Fibre Channel         iSCSI           Average Savings

Host Initiator   $800-$1800         $0-$600             77%
Switch Ports     $400-$1800        $25-$800             63%
Total Costs     $1200-$3600        $25-$1400            70%

Eric R. Schott is director of product management at EqualLogic, Inc. (Nashua, NH)

www.equallogic.com