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Special-purpose adapters for iSCSI, a sample of native iSCSI storage offerings and more.

Where is iSCSI technology today?
2003 witnessed two major milestones in the technical evolution of iSCSI: The Internet Engineering Task Force approved the final draft of the iSCSI standard, meaning that vendors now have a defined target to focus their development efforts. The other major event was the release of officially supported iSCSI software drivers from Microsoft Corp. This support for a major commercial platform provided a validation to many that the technology is truly viable and will likely have a promising future. In addition, some major storage vendors such as EMC Corp. and Network Appliance Inc. (NetApp) have started offering some level of direct iSCSI attachment to their storage systems. Microsoft recently announced the first group of devices that have been qualified with its driver.

Is iSCSI technology ready for prime time? The short answer is yes and no. Yes, because more products and standards are entering and stabilizing the market. No, because IP SANs bring many implementation issues to the table that are new to storage. Consider, for example:

Host connectivity: In iSCSI (and traditional SCSI) parlance, the host requesting service is an initiator and the device providing that service is a target. An iSCSI initiator can be either a hardware device or a software driver. Today, drivers for host iSCSI connectivity are readily available for Windows and Linux hosts. Although at least one vendor, Cisco Systems Inc., offers drivers for some Unix platforms, most midrange and high-end systems haven't started providing support in the iSCSI arena. These software initiators require only a NIC. For performance reasons, it's generally expected that GigE will be the common connection for iSCSI, but aside from performance, traditional 100Mb NICs should also work.

Hardware interfaces are available from a number of vendors. These devices include iSCSI HBAs, as well as gigabit NIC cards equipped with TCP/IP offload engines, known as TOE NICs. (See "Special-purpose adapters for iSCSI")

Networking: Because iSCSI is a TCP/IP-based protocol, there's no need for special switches to support it. Traditional IP switches and routers process iSCSI packets in much the same way that they handle other network traffic. However, one significant opportunity for iSCSI deployment is to provide broader host access to existing FC storage. To accomplish this, an IP/FC gateway or switch is needed. Some vendors, such as Cisco, McData/Nishan and Sanrad, provide products to perform this function. These devices include some GigE ports with at least one FC E-port (and possibly N-ports). See "IP-FC gateway devices" for details on some of the options available for IP-FC interoperability.

Storage: Until recently, the iSCSI storage market consisted primarily of emerging vendors. While some major storage vendors have introduced iSCSI support, others have been slow to enter the market (see "Sample of native iSCSI storage offerings").

Where to use iSCSI
It's clear that the technology needed for successful deployment of an IP SAN is available today. The next consideration is what the appropriate uses for the technology are, and where it will provide the most benefit.

Prior to iSCSI/IP SAN technology, the conventional way to retrieve and write data via the IP network was by file access (conventional file servers and network-attached storage appliances). Applications--such as databases and some e-mail products--that access data by blocks preferred DAS or an FC SAN. With iSCSI, these applications can now be supported over the LAN.

Providing file- and block-level data over the same transport can simplify storage management. Utilization can also be improved because storage can be more readily shared and allocated by function (see "Shared storage in an IP SAN"). Additional benefits can also be realized in improvements to availability. With LAN access to storage, a variety of options relating to clustering of nodes and replication of data become more viable.

IP SANs also present new options for backing up data. Administrators now have the option to do traditional file-based backups across the network to a backup server or to perform image-based backups directly to shared tape devices. While similar to traditional LAN-free backup, the increased flexibility of IP provides a greater opportunity to deploy this option.

Management questions
As IT organizations begin to deploy iSCSI, they will need to develop additional capabilities to manage these new technologies. However, organizations actually start from an advantage that early adopters of FC SANs didn't have. Today's IT networking staff has already developed strong capabilities to configure, maintain and monitor IP network infrastructures. Likewise, expertise previously gained by managing storage in FC SAN environments can be readily applied to iSCSI storage.

Many comprehensive management tools are available to monitor and configure an organization's IP network infrastructure. However, expect tools that assist in managing the iSCSI layer to be relatively limited in the early stages. As IT organizations implement IP SAN technologies, new tools will emerge and existing SAN management solutions will integrate iSCSI configuration and monitoring capabilities into their offerings.

This was first published in December 2003

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