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Choosing a SAN technology: Fibre Channel vs. iSCSI

What you will learn in this tip: Part one and part two of our series discussed the

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specific features of Fibre Channel storage area networks (SANs) and iSCSI SANs. Part three of our series will discuss Fibre Channel vs. iSCSI SAN misconceptions. We clear up the myths about Fibre Channel vs. iSCSI to help you choose the best SAN technology for your organization.

There are a many misconceptions about Fibre Channel and iSCSI SAN technologies. Several are perpetuated by the vested interest of specific storage vendors. Some of these SAN technology misconceptions have a grain of truth but are tainted by the past, not the present. Other misconceptions are correct on a technical basis but have no relevance in the real world. This article clears up some of the most common misconceptions about Fibre Channel vs. iSCSI SANs and also helps you choose which technology is best suited for your small- to medium-sized business (SMB) environment.

Misconception #1: Fibre Channel SANs are faster than iSCSI SANs 

Although it's true that 4 Gbps Fibre Channel has a higher throughput than 1 Gbps iSCSI, it's also true that aggregating four 1 Gbps Ethernet ports gets the same bandwidth. And 8 Gbps FC has slightly less bandwidth than 10 Gbps iSCSI. So from a throughput perspective, this misconception has a small kernel of truth based on the low-end bandwidth specs.

Misconception #2: Latency IOPS play a big role in SAN technology

Intuitively, iSCSI latency should be significantly greater than Fibre Channel, because of TCP latency. As latency increases so does response time. Higher latency generally means fewer IOPS. But VMware's fall 2009 testing of NFS, iSCSI, and FC revealed some surprising results. Published in the white paper titled: "VMware vSphere 4: Exchange Server on NFS, iSCSI, and Fibre Channel", the test results showed that iSCSI latency is definitively higher than Fibre Channel, especially on initial load. But it also showed that IOPS were considerably higher on Fibre Channel than iSCSI with the greatest differences coming at initial load. Oddly, as the load over time leveled off, the latency IOPS differences narrowed. There was still a measurable difference, but it was much smaller than expected. So unless it is a very high transaction-oriented application, the latency differences will not matter very much for your small business application.

Misconception #3: iSCSI SANs are always less expensive than Fibre Channel SANs 

iSCSI SANs are often seen to be less expensive than Fibre Channel SANs. And when you compare 1 Gbps iSCSI vs. 4 Gbps Fibre Channel, iSCSI is less expensive in terms of acquisition and maintenance costs. The iSCSI hardware, especially at the port level where no TCP/IP offload is required, is also less expensive than Fibre Channel. However, one misleading argument is that iSCSI can also run on current infrastructure. Although iSCSI can be run over existing switching and IP infrastructure, it is not recommended. Performance is likely to be severely degraded, unpredictable, and less secure if not operated on a dedicated network or subnet (LAN or VLAN).

But comparing the costs on a per gigabits-per-second basis narrows the cost differences between iSCSI and Fibre Channel considerably. Often, a 10 Gbps iSCSI SAN costs more than a 8 Gbps Fibre Channel. This is even true for the initiator ports, target ports, and switch ports. Performance levels also make a difference in costs. At lower performance levels (1 Gbps iSCSI vs. 4 Gbps Fibre Channel), iSCSI requires considerably less CapEx than Fibre Channel. At higher performance levels (10 Gbps iSCSI vs. 8 Gbps Fibre Channel), iSCSI actually requires somewhat more CapEx. OpEx differences are more pronounced.

Furthermore, training costs differ between iSCSI and Fibre Channel as well. Fibre Channel SAN technology is new for most storage administrators and therefore requires more training costs and a relatively long learning curve. It is not intuitive. Add this to the deterministic manually intensive nature of Fibre Channel and the OpEx costs are considerably higher than iSCSI.

Overall, the costs for Fibre Channel and iSCSI SANs differs for each company. An iSCSI SAN can be more expensive than a Fibre Channel SAN and vice versa, but keep in mind that the difference in cost is often much narrower than expected.

Misconception #4: iSCSI SANs simpler to operate vs. Fibre Channel SANs 

Few dispute this fact that iSCSI SANs are easier to operate than Fibre Channel SANs because of the non-deterministic, discoverability, and routing of TCP/IP Ethernet networks. Also, network implementation, operations, management and change management is far more automated and forgiving on iSCSI SANs than FC SANs. But this conventional wisdom is based on information from the past, not the present.

Recent advances in small and medium Fibre Channel SANs have made implementations, operations and management on an ease of use parity with iSCSI. Larger environments are still far more complicated than iSCSI, but even change management for Fibre Channel SANs can be handled on a more simplified automated basis with products from Aptare Inc., NetApp Inc., SANpulse Technologies Inc. and TekTools (now part of SolarWinds). And boot from SAN is actually simpler on a Fibre Channel SAN vs. an iSCSI SAN (which requires at least one separate DHCP server and usually two for HA, offering up a PXE or boot up image.)

So which SAN is right for your SMB?

There is no "right" SAN technology for your SMB environment. Both Fibre Channel and iSCSI SAN are up to the task. Generally, the iSCSI SAN tends to be a bit simpler with somewhat lower costs; whereas the FC SAN tends to be somewhat faster with lower latencies/higher IOPS. But after going through common misconceptions, these statements aren't always true. The right choice boils down to your organization's unique requirements, knowledge, experience and comfort level.

About the author: Marc Staimer is the founder, senior analyst, and CDS of Dragon Slayer Consulting in Beaverton, OR. The consulting practice of more than 12 years has focused in the areas of strategic planning, product development, and market development. With over 30 years of marketing, sales and business experience in infrastructure, storage, server, software, and virtualization, he's considered one of the industry's leading experts. Marc can be reached at marcstaimer@mac.com.


 

This was first published in September 2010

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