In the beginning there was Fibre Channel (FC), and it was good. If you wanted a true SAN -- versus shared direct-attached SCSI storage -- FC is what you got. But FC was terribly expensive, requiring dedicated switches and host bus adapters, and it was difficult to support in geographically distributed environments. Then, around six or seven years ago, iSCSI hit the SMB market in a big way and slowly began its climb into the enterprise.
The intervening time has seen a lot of ill-informed wrangling about which one is better. Sometimes, the iSCSI-vs.-FC debate has reached the level of a religious war.
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This battle been a result of two main factors: First, the storage market was split between big incumbent storage vendors who had made a heavy investment in FC marketing against younger vendors with low-cost, iSCSI-only offerings. Second, admins tend to like what they know and distrust what they don't. If you've run FC SANs for years, you are likely to believe that iSCSI is a slow, unreliable architecture and would sooner die than run a critical service on it. If you've run iSCSI SANs, you probably think FC SANs are massively expensive and a bear to set up and manage. Neither is entirely true.
Now that we're about a year down the pike after the ratification of the FCoE (FC over Ethernet) standard, things aren't much better. Many buyers still don't understand the differences between the iSCSI and Fiber Channel standards. Though the topic could easily fill a book, here's a quick rundown.
The fundamentals of FC
FC is a dedicated storage networking architecture that was standardized in 1994. Today, it is generally implemented with dedicated HBAs (host bus adapters) and switches -- which is the main reason FC is considered more expensive than other storage networking technologies.
As for performance, it's hard to beat the low latency and high throughput of FC, because FC was built from the ground up to handle storage traffic. The processing cycles required to generate and interpret FCP (Fibre Channel protocol) frames are offloaded entirely to dedicated low-latency HBAs. This frees the server's CPU to handle applications rather than talk to storage.