Many companies in the storage channel, especially those selling into the SMB market, are trying to decide whether which storage technology to focus their energy on. One option is a storage area network (SAN) based on the iSCSI standard to move block-level data to storage devices. The other is to continue with network attached storage (NAS) using the file-based standards of NFS and CIFS.
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When considering which storage options to sell and support, resellers have to ask themselves some tough questions. Which storage network would be easier to work with and sell? Where can I make more money? Which would bring greater benefit to my customers?
These are just a few of the questions resellers grapple with. My question back to these resellers is, "why leave money on the table? Why not provide both?"
Both iSCSI and NAS (NFS/CIFS) storage protocols use the same fabric already found in customer's environments: TCP/IP over Ethernet. Most customers are already comfortable with Ethernet, even if they are not experts on how to use their infrastructure to build a flexible, secure storage network. Using iSCSI and NAS protocols to build a network storage infrastructure leverages the knowledge, management and process customers already in place.
iSCSI SAN and NAS differences
The differences between iSCSI SANs and NAS are really not that great. Both can use standard Ethernet network interface cards (NICs) at the host end and standard Ethernet switches within the network. The differences come on the host system and on the storage.
NAS protocols require support for NFS (usually on UNIX/LINUX-based systems) or CIFS (on Windows systems) on the host system as well as on the NAS server. NFS and CIFS interoperates with the operating system to create pointers to the files that are not located on a local (or SAN) storage device. Interactions for both systems are done at a fairly high level within the operating system.
Similarly, iSCSI SANs require support at both the host and storage sides of the network. iSCSI encapsulates the SCSI protocol (often used with local storage) within an IP packet down at the driver level of the operating system. This can be implemented either in the form of a software initiator that is loaded on the host system, at the hardware level in the form of a hardware initiator or a special NIC with the iSCSI protocol embedded upon it.
The storage side must also support the iSCSI protocol with an iSCSI target. The iSCSI Protocol interfaces at a lower level within the operating system and, unlike NAS, does not interact with the data at a file-level, but rather, at a block level. To the operating system, iSCSI SAN storage looks like local storage. Once the SAN or NAS connections have been set up and configured, access to the data located on the networked storage is transparent to the user, to a point. That point being how fast data can get to applications.
Increasing iSCSI SAN and NAS performance
There are a variety of solutions to address the performance of iSCSI SANs and NAS storage solutions today. These solutions provide a variety of price/performance options for both the resellers and customers. Some of the solutions can increase performance for both NAS and iSCSI SAN implementations at the same time.
One quick and easy way to increase the performance of both NAS and iSCSI is to use high-speed NICs. Rather than running a storage network with 10/100 NICs, upgrade to 1Gb or even 10 Gb. With iSCSI SANs, the least expensive implementation is done using a software initiator (you can get software initiators off the net for free). However, this is the lowest performing solution because everything is done in software.
To gain performance at a little higher price, resellers can offer a iSCSI host bus adapter (HBA). This is a network interface card that has had the iSCSI initiator embedded in the hardware (or firmware) to provide iSCSI acceleration.
Often included on these HBAs is a TCP Offload Engine (TOE) which offloads the TCP/IP processing from the host CPU onto an adapter. TOEs significantly increase performance by processing IP packets in the hardware rather than the software within the operating system These adapters are available at many different speeds, from any number of vendors including Adaptec and Qlogic.
Finally, the Internet Engineering Task Force (IETF) recently ratified extensions to the Ethernet standard called iWARP. These extensions specifically address Ethernet performance. Instances iSCSI and NAS requiring the highest levels of performance can use adapters that have implemented the entire set of iWARP extensions. These capabilities, taken together, can provide a variety of price/performance offerings to meet a wide range of IP-based storage solutions using iSCSI and/or NAS.
Pricing iSCSI SAN and NAS upgrades
For everyone used to purchasing 1Gb NICs for about $100 per port with no special features, seeing suggested retail prices ranging from $400 to over $1000 for all these features might be cause for thought. But think about this: With each advancement in Ethernet, the cost of adapters start high but quickly comes down. Providing solutions using both iSCSI and NAS will allow you to offer a broad range of solutions and services to a wider range of customers. So, why not provide both?
About the Author: Anne Skamarock has been involved with computers and associated technology for nearly 30 years. She started her career as a software engineer developing custom scientific codes and as a UNIX systems administrator. She moved over to the systems vendor side and has worked as a software engineer, technical sales, marketing and management for both large and start-up systems and storage companies such as SRI, International, Sun Microsystems, Solbourne Computer, and StorageTek. For the past seven years, Anne has worked as a market analyst focusing on the convergence points around systems, storage, and software. Anne has published extensively including regular columns and tips for TechTarget's SearchChannelStorage.com and Network World, and numerous business and technical white papers. She has recently finished her second book as co-author of Blades and Virtualization: Transforming Enterprise Computing While Cutting Costs.