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iSCSI vs. Fibre Channel: What is best choice for your SAN?

It's the battle of the century. In the blue corner, promoted by every major server and storage vendor wearing 2 Gbps, 4 Gbps or 8 Gbps adapters is Fibre Channel. In the red corner, promoted primarily by network-attached storage

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(NAS) vendors, startups and users wearing 1 Gbps or 10 Gbps network interface cards (NICs) is iSCSI. Have you had enough of the hype?

The trade press has positioned these two storage area network (SAN) technologies as fierce competitors. In contrast, major server and storage vendors prefer the iSCSI SAN as an adjunct to Fibre Channel SANs.

 

Cutting through the layers of obfuscation brings into focus a slightly different reality. Both iSCSI and Fibre Channel technologies solve the same technical problem of networking block storage. The differences are in the details. There are five areas to consider when picking a SAN technology:

Performance/reliability
Complexity/ease of use
Manageability
Total storage SAN solution
Total cost of ownership (TCO)

Performance

Fibre Channel is a layer 2 switching technology or cut through, with the protocol handled entirely in hardware. The iSCSI protocol (SCSI mapped to TCP/IP) running on Ethernet is a layer 3 switching technology with the protocol handled in software, hardware or some combination of the two.

Fibre Channel is often touted as the high-performance, more reliable SAN technology. Early in iSCSI development that was definitely true, but that's not exactly true in 2008. The mythology hasn't kept up with the veracity.

On paper, 4 Gb Fibre Channel should have nearly four times the performance of software-based 1 Gb iSCSI. Tests performed by the Enterprise Strategy Group (ESG) and confirmed by users demonstrate software-based 1 Gb iSCSI performs at approximately 80% to 85% of the throughput and IOPS of 4 Gb Fibre Channel (or put another way, Fibre Channel has 20% to 25% higher throughput and IOPS). This is a far cry from the perceived differences.

Performance bottlenecks are far more likely to be the result of the target storage (interface, controller que depth, controller clustering, number of disks, disk type, etc.), the physical server or the SAN fabric oversubscription rate (number of server initiators to number of storage target ports), than the SAN technology.

With the emergence of 10 Gb iSCSI and 8 Gb Fibre Channel, the "perceived" paper-based performance potential moves into the iSCSI corner. It will even out later this year with the release of Fibre Channel over 10 Gb Ethernet (FCoE).

So which technology is the better performer? All things being equal, Fibre Channel should be marginally better in IOPS (because of lower latency) and throughput (because of lower overhead).

Complexity/Ease of use

Because the iSCSI SAN is based on the well-known TCP/IP and Ethernet, it's far simpler and less complex than Fibre Channel. The learning curve and expertise requirement for Fibre Channel is measurably higher. Fibre Channel tends to be significantly more manually intensive vs. iSCSI, which has a lot more built-in automation. As a result, Fibre Channel technology usually requires more training, a greater knowledge base and ultimately higher costs with both.

Manageability

Hands down, iSCSI SANs are far easier to implement, operate and manage than Fibre Channel. ISCSI leverages the vast capabilities of TCP/IP and Ethernet and is much less expensive. Most moves and changes are performed online and aren't disruptive to applications.

Although Fibre Channel has come a long way in manageability, the majority of moves and changes are application disruptive. This means they must be scheduled and performed offline. The alternative is to live with the application disruptions, and in some cases, deal with potential data loss.

Total storage SAN solution

This is the complete end-to-end package including the storage system, the storage software (snapshot, mirroring, thin provisioning, etc.) and the SAN. There are considerably more Fibre Channel-based packages today than iSCSI. However, many of the iSCSI packages from younger vendors (3PAR Inc., Agami Systems, Dell EqualLogic, LeftHand Networks Inc., Nimbus Data Systems Inc. and Reldata Inc.), are based on newer technology and capabilities (clustered storage, thin provisioning, more automation, 10 Gb iSCSI, etc.).

TCO

TCO includes the acquisition costs, installation costs, professional services costs (if any), additions/upgrade costs, management costs, operational costs, maintenance costs, subscription costs, power, cooling and real estate cost. These costs apply to the storage system, the SAN and the storage software.

Fibre Channel vendors have done a pretty good job in reducing the costs of their solution. Unfortunately, these solutions have a considerably higher TCO than equivalent iSCSI solutions. The adapters, switches (and especially the data center class switches called directors) and software all have considerably higher TCO than their iSCSI equivalents.

So in the end, how do you pick your SAN? The answer is: "It all depends." Choose the technology that best meets your requirements of performance, ease of use, manageability, total package and TCO.

About this author: Marc Staimer is President and CDS of Dragon Slayer Consulting in Beaverton, OR. He's widely known as one of the leading storage market analysts in the network storage and storage management industries. 


This was first published in May 2008

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