At issue: If you have an iSCSI SAN, chances are you that you aren't using iSCSI HBAs. But maybe you should: At...
least one user says that the performance boost is worth the slightly bigger price tag.
Home iSCSI users will tell you that you don't really need iSCSI host bus adapters (HBAs), specialized cards that can offload TCP/IP and iSCSI processing from a server's CPU. These users say that software-based iSCSI initiators are sufficient for most applications.
Of the 1,500 or so iSCSI SANs in the world, fewer than 10% of them are using iSCSI HBAs, says Tony Asaro, senior analyst with the Enterprise Strategy Group, Milford, Mass. Nevertheless, one iSCSI adopter says that installing HBAs in servers connected to their iSCSI SAN has given them all the performance they need, added minimal cost to the overall environment and provided peace of mind.
Mike MacNeill is director of technical operations for Cross Country Healthcare, Boca Raton, Fla., which matches healthcare workers with temporary staffing opportunities. Last year, the company decided to deploy a SAN for its Windows and Linux application servers, including file serving, Exchange and SQLServer to get better disk utilization and improve its backup process.
The company already had an IBM FAStT array in place for its IOPS-intensive IBMAIX applications, and based on those performance demands, MacNeill knew that a Fibre Channel SAN would be overkill. "These are performance-hungry servers, and they only take up a fraction of the 2 Gbps pipe." Instead, they chose to buy a pair of Network Appliance 940c filers and run iSCSI.
For his servers, MacNeill tested both software and hardware-based iSCSI initiators. He tested a Linux initiator that he found on the open-source software site freshmeat.net, but even though the initiator performed well, he worried about support. "For certain things, I want someone to call," he says.
The Microsoft iSCSI initiator also performed well, resulting in about 9% to 10% CPU utilization. Cross Country probably could have gotten away with using it, but ultimately, "I'd rather get my initiator from a hardware vendor than from Microsoft," MacNeill says. "Software screws up more often than hardware," he says, and he prefers to "have storage processed at a lower level."
The hardware initiators MacNeill tested were the Intel PRO/1000 T IP Storage Adapter and the Adaptec 7211C. The Intel card, MacNeill found, was outperformed by Microsoft's software-based initiator, while the Adaptec card resulted in maximum CPU utilization of 3%, with 1% to 2% as the norm. Besides the card's performance, "I like the Adaptec name; I've trusted them all this time to do SCSI," MacNeill says.
MacNeill purchased the cards from CDW.com for about $500 apiece. But even with the cost of the iSCSI HBAs, MacNeill estimates that he saved Cross Country Healthcare around $40,000 by avoiding Fibre Channel HBA, switch and cabling costs. All in all, MacNeill says, "I really don't understand why more people aren't using iSCSI."
For more information:
Tip: Pound-foolish iSCSI: Should you use NICs IN SANs?
Tip: How to tweak Ethernet for iSCSI SANs
Tip: Dueling SAN technologies: NAS vs. iSCSI
About the author: Alex Barrett is "Storage" magazine's trends editor.