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The performance question
The motivations for going with IP storage are as different as the organizations using the gear--but there are some constants. Performance was an issue for some companies. Most of the companies interviewed are using Gigabit Ethernet switches, network interface cards (NICs) and associated gear, and have put their IP traffic onto its own VLAN for both performance and security considerations.
The Denver Museum of Nature & Science's Wolfe says flat-out that "there's a performance hit if the network's really busy."
Other adopters, though, say they have no complaints on the performance side. Helen Chen, network researcher at Sandia National Laboratories, says she has seen peak performance of 180Mb/s over its IP network for a write function. "I believe iSCSI has the potential to deliver performance for scientific computing," she says. The lab has already proven that IP performs "as well as Fibre" in a local connection "if we tune it correctly."
The lab is also more interested in open-source solutions. On the hardware side, the problem is that "you can't tune hardware very easily" to do things like increase the distance between initiator and target, Chen says. "So, we used the software stack in the Linux host to modify parameters," including iSCSI command size, TCP/IP window size, etc. "We want to open up the parameters so we can fill up a big, fat pipe between two remote locations," she says. "We're
PBS, Alexandria, VA, uses a StoneFly IP concentrator to network the storage for the applications that don't require the highest bandwidth provided by its other SAN, based on FC. They're "quite pleased" with IP's performance, but Ken Walters, senior director of enterprise platforms, emphasizes that not all applications are natural fits for iSCSI. "I use it for equipment used for development work, and on machines that aren't critical or that don't have massive I/O requirements." These are applications that "I can't cost-justify connecting to my Fibre SAN," he says.
And so, he says, PBS is starting to provide iSCSI storage where they really need it. Some of the applications connected via the StoneFly device are a Linux box that processes the logs from the PBS Web site and a SQL Server cluster that's a development environment for an internal PBS user. Walters' group recently received an iSCSI cluster router from StoneFly. "I wanted to get clustering set up before I handed out a lot more storage because I didn't want a single point of failure," he says.
"So now, we'll start to provide iSCSI storage where appropriate." The organization uses the StoneFly Concentrators to stream all Real and Windows media from the Web site.
At Zenon Environmental in Ontario, Canada, Shawn Eveleigh, senior systems administrator, says he's happy with his PeerStorage setup from EqualLogic. He used utilities in Exchange that test how fast a disk subsystem performs. "Our total disk I/O speed was around 40 to 45Mb/s, and most of our systems will never get to that kind of load," he says. "That was forcing the server to go as fast as it possibly can. And the disk I/O kept up with that."
Designing for performance
Almost all the organizations we talked to are using standard-issue, out-of-the-box Gigabit Ethernet NICs, but PBS is an exception. The group is using a combination of regular NICs and cards that offload part of the IP and iSCSI processing load from the server. These include Intel Storage Network Interface Cards (SNICs) and TOE cards from Alacritech and other suppliers. "The offload does work as advertised," PBS' Walters says.
Which type of card he uses to hook up each server to the SAN depends on how much processing power the server has to deal with iSCSI's additional workload. "Much of our hardware is fairly new," he says, "with plenty of processing power. So, I use mostly regular NICs, for about $130, where SNICs are about $550 and TOEs are around $850."
There are some nitty-gritty things to consider for performance, too. Akil Woolfolk, network operations team lead at Atlanta-based mortgage lender HomeBanc, says they had to make registry changes to make sure SQL Server works well with iSCSI. "We had to do some configuration to create a dependency" to make sure the SQL Server wouldn't start before the iSCSI initiator was up and running," he says. Otherwise, the SQL Server will crash because some of the files it needs to see aren't present.
Also, Woolfolk and his team at HomeBanc figured it was wise to plan where to put each application's database associated log files. "That makes a difference in your implementation," he says. "We put the log files on the local disk, with the OS to help boot up storage. Then, we run the iSCSI initiator to connect the servers to the IP SAN."
HomeBanc is using EqualLogic's PeerStorage to host file services for more than 500 users, with more than 80% of its production SQL data on the IP SAN.
This was first published in April 2004