Anyone who has considered crossing the bridge from DAS to a SAN has faced a fundamental choice between two technologies: the established, but pricey FC (Fibre Channel) and the more affordable but still emerging iSCSI (Internet SCSI) transport.
According to the sales numbers, this is clearly a lopsided war. IDC says that 2004 sales of iSCSI systems generated worldwide revenue of only about $113 million, a tiny drop of less than 2 percent in the $7.6 billion SAN bucket, which is nearly full with FC gear. The dominance of FC ensures that customers can pick and choose from a multitude of accepted, proven FC solutions.
On the iSCSI side, simplicity and low cost of deployment are the most compelling advantages. Whereas connecting a server to an FC network requires installing an expensive HBA plus its drivers and management software, connecting a server to an iSCSI network can be accomplished with a Gigabit Ethernet NIC, already present on most servers. An iSCSI initiator -- an application that enables access to a remote volume via an Ethernet connection -- is also required, but on most platforms, it’s free.
The added cost of FC has limited its deployment on the low end. “In the sub-$25,000 server market, FC is used less than 5 percent,” says Brian Reed, vice president of business development at Emulex.
That cost gap is shrinking, however, because vendors such as Brocade, Emulex, and QLogic have come up with FC HBAs and switches that target the SMB market with a combination of lower price, easier administration, and a somewhat reduced set of customization options. In fact, a budget FC HBA now costs roughly the same as an iSCSI HBA, which many customers choose over a standard Gigabit Ethernet connection plus software for performance reasons.
Another important point in favor of FC is the nominal transfer rate: 2Gbps (with 4Gbps coming soon) for FC versus 1Gbps for iSCSI. That gap is not so significant for end-to-end connections, where the server or the storage device is usually the slow link. It does, however, begin to make a real difference as multiple switches pile up in a storage fabric.
Ironically, although iSCSI advocates often tout the future leverage of affordable and compatible 10 Gigabit Ethernet, until now the only low-cost product to offer 10Gbps connectivity has been the SANbox 5200, an FC switch from QLogic.
Regardless of speed, iSCSI will certainly gain more traction in the future, with the bulk of future deployments probably appearing in smaller datacenters.
“It’s not a matter of do I use iSCSI or do I use FC, but more of an issue of which one do I want to use where,” says Tom Nosella, director of engineering for the storage switching group at Cisco. For example, companies with ubiquitous FC may choose the more affordable and WAN-friendly iSCSI for servers needing only occasional access to a storage pool -- especially remote locations that lack local FC expertise.
For many organizations, the choice boils down to the price of talent. The cost of hiring or training FC experts is still enormously greater than getting iSCSI help, a key factor for those just stepping up to a SAN. But that cuts both ways. If the FC talent is already there, given the drop in FC hardware prices, larger organizations have little reason to turn away from the high performance and long, reliable track record of FC.