The key component in the unified data centre is lossless Ethernet, according to FibreChannel and iSCSI advocates. Yet there is a religious war brewing between the two camps on the best way to integrate storage into an Ethernet-based unified data centre fabric.
"Everybody thinks that if you go against iSCSI or you go against FibreChannel, you're a bigot one way or another," says Craig Chapman, director of Cisco Unified Computing System strategy at systems integrator MCPc in Cleveland, Ohio. "You can't be a protocol passionista. You can't be tied to one way of doing things. It's, 'What's best for the solution based on what you've seen? And you've got to balance those out."
Chapman says iSCSI does not compete with FCoE as a method for unifying a data centre fabric. Both have their place, especially if an enterprise has an installed base of one or the other.
FibreChannel is usually preferred by larger enterprises with a low tolerance for latency and packet loss, and a requirement for high application throughput. But it requires its own infrastructure, which drives up its cost.
Smaller and mid-size enterprises might opt for the less expensive iSCSI, which is more latency tolerant than FibreChannel and "lossy," Chapman says.
"You will see iSCSI in enterprises, especially for replication solutions and for remote office installations," says Steven Scully, research manager for Continuity, Disaster Recovery and Storage Orchestration at IDC. "At the core, those customers will be the big FCoE users. On the other hand, you probably won't find much FCoE in SMB customers."
Since it runs over TCP/IP, iSCSI is susceptible to TCP "overhead," such as the windowing characteristic in TCP, Chapman says. A TCP window is a chunk of data, made up of several packets, sent by a server. After the server receives an acknowledgement from the client that the window has been received -- without errors -- it will send the next window of packets.
If errors occur, the data must be resent. This whole event can introduce latency and packet loss with iSCSI, Chapman says. But nothing precludes a business from converging or unifying servers, storage and networking in a data centre with iSCSI -- indeed, Cisco says its can transport iSCSI over Ethernet just as capably as FibreChannel over Ethernet.
And 10Gbps iSCSI converged network adapters are appearing on the market from Network Interface Card vendors such as Emulex.
Yet FCoE garners most of the hype and press coverage because of Cisco's emphatic endorsement of the technology for unifying data centers -- and because it's newer than iSCSI. FCoE was standardized less than a year ago while iSCSI is at least 10 years old.
Indeed, Cisco acquired its way into iSCSI with the 2001 purchase of NuSpeed, an iSCSI router start-up. Cisco has since killed off the NuSpeed product, which was called the SN 5420.
"iSCSI we saw -- and it played out this way -- as more of a small-business play, where there was such a large entrenched base of FibreChannel that was projected by the analysts to continue to grow," says Jackie Ross, vice president of marketing in Cisco's Server Access and Virtualization Group. "We couldn't ignore that."
And iSCSI is even losing ground to network-attached storage (NAS) in the SMB market because SMBs are now opting for file-based storage -- which NAS supports -- vs. block-based storage, which iSCSI and FibreChannel support, Ross says.
"For SMBs, NAS -- or file-based storage -- has grown up as their needs have grown up," Ross says. "With some of the needs you could only get in block-based storage -- disaster recovery, much better management of multiple networks -- you can now get with file-based storage. That's the reason NAS has grown at double the rate of iSCSI."
But there's still healthy growth in iSCSI. It's growing at about 25% per year for companies that have not opted for NAS over direct-attached storage, Ross says.
According to Dell, the market leader in iSCSI SANs, it's even healthier than that. According to IDC, the iSCSI SAN market grew 40.6% year over year in the fourth quarter of 2009. Dell led that market with 29.2% revenue share, followed by HP with 18.5%. And Dell's EqualLogic iSCSI product line - Dell acquired iSCSI SAN vendor EqualLogic in 2007 -- grew 44% in that period.
For the full year 2009, spending on iSCSI storage gear was $1.9 billion, according to IDC, growing to $4.4 billion in 2013 -- a compounded annual rate of 23.4%. Users spent $9.2 billion on FibreChannel/FCoE/Inifinibad gear in 2009, and that will grow to $11.1 billion by 2013 -- a CAGR of less than 5%, according to IDC.
Meanwhile, Dell says it recently commissioned Forrester Research to conduct a survey of the storage and unified fabric plans of 213 companies. According to Dell, the survey found that two-thirds of respondents are moving toward a unified fabric in one to three years; and of those with awareness or knowledge of unified fabric, 56% believe iSCSI is best suited while 27% believe FCoE is best suited.
Regarding storage purchases in the next 12 months, 10GbE and iSCSI arrays are the top two selections, Dell found in its survey. Among all survey respondents, 45% planned to purchase 10GbE switching or related components, while 39% planned to purchase iSCSI arrays.
Dell is encouraged by these findings and its position in the iSCSI market as customers consider converged data centre fabrics.
"If you're looking to make a unified fabric decision today, you're looking at iSCSI, which has been around for … years now," says Travis Vigil, senior manager, Dell, who is responsible for the EqualLogic iSCSI storage portfolio. "There's years of testing and validation, real-world customer deployments behind it, and it allows you to unify your fabric at 1Gbps and 10Gbps. So it gives you more flexibility than what you may be able to realise with other technologies."
Both Vigil and Ross agree, though, that the religious wars are missing the point: the real unifier in the converged data centre is a lossless version of Ethernet with flow control capabilities, which is being standardized now in the IEEE's Data Center Bridging task group.
"We violently agree on the 'over Ethernet' part," Vigil says. "Whether customers deploy iSCSI over that or FCoE is the next choice."
And the Data Center Bridging enhancements to Ethernet will benefit iSCSI just as much as FCoE in making the converged fabric lossless, low latency and more reliable, Vigil says.
"The difference is, (the DCB enhancements) are required for FCoE whereas for iSCSI you have flexibility in that they're not required -- but they do help in terms of providing more predictable performance in converged infrastructures," he says.
"We always find it a little challenging when people say it's one or the other -- no it isn't," Cisco's Ross says. "It's making sure that you have the right fabric in place that's going to be able to support any choice that you want and that you may have in your environment already."
So can iSCSI be used to converge your storage facilities with your servers and network as long as you have a lossless Ethernet fabric?
"I certainly think so," says Frank Berry, CEO and senior analyst for the Unified Networking Practice at IT Brand Pulse, a data center market analysis firm. "It depends on who the audience is."
Berry expects revenue from iSCSI storage to exceed revenue from FibreChannel storage within five years.