Fibre Channel background
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Fibre Channel was developed in the late 1980s and ratified as an American National Standards Institute (ANSI) standard in 1994. It is now a mature technology that provides a high-performance, high-speed switched storage network using dedicated host, switch and storage hardware. Fibre Channel SANs were introduced to improve connectivity between storage and hosts, consolidate storage systems and improve performance.
iSCSI background
iSCSI, only ratified in 2003 by the Internet Engineering Taskforce (IETF), is a low cost IP-based protocol for connecting storage and hosts using existing or dedicated IP networks. iSCSI was developed to address the need for a more cost-effective alternative to Fibre Channel; IP networking technology is inherently cheaper than Fibre Channel (more later). Both iSCSI and Fibre Channel connect host and storage using the standard SCSI command set and therefore provide block-level access to data.
Determine SAN requirements
Before offering any solution, ask your customer what it is they require.
- Availability: What level of availability is required for the SAN? Is it critical that the SAN be available at all times, or is downtime for maintenance or equipment failure tolerable?
- Performance: What level of performance is required from the SAN? Is data throughput by the host an important factor? Is total throughput of the SAN an important factor?
- Applicability: What type of data is the SAN being used for? Is it mission-critical production data or a development environment?
Match requirements to SAN constraints
Once requirements are understood, these should be matched to the constraints of each technology type.
- Cost of equipment
Fibre Channel: FC equipment is considerably more expensive than iSCSI. Host bus adapters (HBAs) can cost approximately $500 to $1,000 each. Fibre Channel switches (or directors for higher availability) cost around $1,000 per port connection.
iSCSI: iSCSI can use standard Ethernet network adaptors and IP switches of much lower cost. - Cost of management
Fibre Channel: FC SANs cost more to administer than iSCSI SANs. There is a higher cost for management software; skilled FC SAN professionals are expensive to recruit and train.
iSCSI: iSCSI uses standard networking technology and can be implemented by IT professionals within an organization who are already familiar with IP protocols. - Reliability
Fibre Channel: FC has a proven record in reliability. FC switches are engineered for high availability (director-class switches offer 99.999% availability) and vendors perform extensive testing to provide certification of HBA, switch and storage array products. In addition, Fibre Channel drivers and support for additional recovery and reliability features such as multipathing is well established.
iSCSI: iSCSI can be implemented across standard network technology and the vendor certification process is not as rigorous; it is therefore less reliable than Fibre Channel when considered for mission-critical applications. - Platform support
Fibre Channel: FC is supported across a wide range of operating systems and applications.
iSCSI: iSCSI currently has narrower support by platform. For instance, only Sun Solaris 10 onward supports iSCSI natively.
Choose a SAN solution
It isn't possible to say exactly which SAN type will meet each customer requirements as needs will differ subtly from customer to customer. However, here are a few general guidelines to make the decision easier.
About the author: Chris M. Evans is an independent storage consultant with Brookend Ltd., with nearly 20 years' experience in a wide range of storage platforms covering mainframe, open systems and Windows. Chris specializes in network-attached storage (NAS) and storage area network (SAN) technologies, designing and implementing large-scale infrastructure projects for major financial corporations. Online, Chris maintains www.storagewiki.com; you can catch up with him on his blog at www.storagegurus.com.
This was first published in January 2007