Is iSCSI good enough?

Organizations of all sizes have adopted iSCSI because it's easy to install, inexpensive, behaves just like Ethernet and doesn't require specialized skill sets like Fibre Channel does. But do analyst claims that iSCSI performance falls short of that for Fiber Channel hold up?

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Users praise their iSCSI SANs, citing low cost, ease of use and better-than-expected performance.


IP SAN adoption is growing among users who want storage that's easy to install, configure and manage, and also comes at a price considerably less than that of Fibre Channel (FC) SANs.

Consider Dave DePillis, manager of IT operations at Allied Cash Advance in Miami, who installed an iSCSI SAN (IP SAN) two years ago to make use of the cabling, switches and network adapters installed in his Gigabit Ethernet network. "Installing iSCSI was absolutely a no-brainer, especially since I had such a small initial investment," says DePillis. He's using iSCSI to back up file shares on four to six virtual machines with Symantec Corp.'s Backup Exec 11 to a Network Appliance (Net-App) Inc. FAS2020 file server. "I have more flexibility with iSCSI since I can use my LAN switches," says DePillis.

James Santillo is another happy iSCSI user. "iSCSI is easy to use and configure," says Santillo, systems administrator at Weiss Group Inc. in Jupiter, FL. He implemented iSCSI capability by installing StorMagic's SM Series iSCSI software on some industry-standard servers equipped with Serial ATA (SATA) drives.


Just what is iSCSI?
iSCSI was adopted by businesses shortly after its ratification by the Internet Engineering Task Force (IETF) in February 2003. The protocol, which was developed within the IETF to transport SCSI commands and block-level data over an IP network between a client and a target device, runs on top of standard Ethernet adapters and over Ethernet LAN or WAN switches.

The technology is implemented by loading a software-based driver--called an initiator--on an Ethernet adapter or by adding a dedicated iSCSI host bus adapter (HBA) to the host computer. Another initiator is added to the target storage array, which allows it to serve up data that will be transported across the network via the iSCSI transport.

iSCSI initiators are available from a number of sources and are categorized by operating system type. Two of the most popular are a Windows initiator from Microsoft Corp. and a Linux initiator from SourceForge (see "iSCSI initiators," below).

Target storage arrays are available from almost every storage vendor, including EMC Corp., NetApp and Overland Storage Inc., among others. Target software--available from vendors such as FalconStor Software Inc., Open-E GmbH and StorMagic--lets users add to commodity servers or gray-box storage arrays from Intel Corp. to make them iSCSI compatible, and so they appear to the client as a local SCSI device (see "A sampling of iSCSI target devices," (PDF) below).

Click here for a sampling of
iSCSI target devices (PDF).

iSCSI can also be implemented with gateway technology in which an iSCSI controller attaches to a block-level storage array, thus enabling iSCSI transport. Examples of gateway-enabled iSCSI products are available from Reldata Inc. and StoneFly Inc.

In addition, a number of vendors have joined the iSCSI and FC worlds with what's called unified or multiprotocol storage. Vendors such as Microsoft, NetApp and Pillar Data Systems market arrays or software that can attach to the Ethernet network as a NAS or iSCSI device, and to the FC SAN.

Various-sized businesses have adopted iSCSI because it's easy to install, inexpensive, behaves just like Ethernet and doesn't require special skills like FC does.

"We don't have Fibre Channel experience," says Scott Christiansen, IT director at Leo A. Daly, an architectural and engineering firm in Omaha, NE. "To get the iSCSI SAN up and running was so quick and easy; it was just unbelievable." Christiansen adds that the SAN "uses the same media as the Ethernet network; it's nice in the sense that everything we buy is Category 6 cable--it works for Ethernet, it works for the IP SAN."

Applications running on iSCSI
A few years ago, many analysts predicted FC SANs would be reserved for business-critical applications such as transactional databases, while iSCSI would be deployed for less business-critical, front-office applications, file shares and Web services. But when talking to users from various-sized organizations, it's clear iSCSI deployments span mission-critical applications and less-demanding office applications.

"Our primary business app runs off a Microsoft SQL Server," says Mike Leather, network services manager at Safeway Insurance Group in Westmont, IL. "Our developers and database administrators were telling me that our disk I/O performance wasn't acceptable; that was because we were growing too big for the original solution [and] we needed to look at something else."

Leather looked at FC SAN storage, but was wary of the challenges and expenses involved. He installed an EqualLogic IP SAN (now owned by Dell Inc.) primarily for his SQL Server environment, but soon found he was using iSCSI for everything. "The whole thing started out for SQL Server and exploded," he says. "We are using the SAN for file storage, Exchange servers and our VMware environment."

Weiss Group's Santillo found that iSCSI will support all of his applications, whether they're business critical or not. "Our custom in-house customer relationship management [CRM] app, which was running on Fibre Channel, is being moved to iSCSI," he says. "We had six SQL Server apps on Fibre Channel, but [they] are now on iSCSI. And we're moving our two Exchange databases to iSCSI. The CRM app is going on the Xiotech box [which is iSCSI enabled]. We're also moving our file systems and unstructured data over to Xiotech," he says. "I needed enterprise-level reliability without the price." Santillo says his six-year-old IBM FC SAN will become "end-of-life'd. We're migrating everything off to iSCSI."


iSCSI initiators
In the early days of iSCSI deployments, almost no one expected iSCSI software initiators to prevail over dedicated iSCSI HBAs.

Adaptec Inc., Alacritech Inc. and QLogic Corp. originally marketed iSCSI adapters complete with features such as TCP Offload, which negates some of the overhead of TCP/IP. These adapters were expensive and often sold for as much as $750, which is four to five times the cost of standard Ethernet adapters.

"We use the VMware and Microsoft iSCSI [Software] Initiator, and we also use iSCSI and Fibre Channel HBAs from QLogic," says Chris Rima, IT systems supervisor at UniSource Energy Corp. in Tucson, AZ. "We've been decreasing the use of the Microsoft iSCSI Initiator because it's not as efficient as the VMware iSCSI initiator or the QLogic iSCSI HBAs. There's a higher cost associated with the QLogic HBA, but it's minimal compared to the performance gains we get."

But other users have overwhelmingly adopted the use of software initiators from Cisco Systems Inc., Microsoft and the open-source community because they're inexpensive or freely downloadable from a vendor's site.

"We use the Microsoft software initiator and it works fine," says Mark Kash, IT specialist for the U.S. Army Corps of Engineers in Huntington, WV. "It's reliable and I haven't had any instances where it's corrupted anything," he says. "Originally, we considered using TOE cards from QLogic because we were thinking a firmware-based platform may be more reliable, but we saved money using the software-based alternative."

Microsoft's iSCSI Software Initiator Version 2.06 is the most popular iSCSI initiator. It supports multipathing for load balancing and failover, 64-bit platforms and IPv6. Multipathing lets the initiator establish multiple sessions with one target, enabling load balancing and failover among multiple network adapters or HBAs.


Is performance good enough?
According to analysts, iSCSI performance would fall short of that of FC. However, end-user experiences don't bear that out.

"We ran some performance tests to see the difference between iSCSI and Fibre Channel, and we saw what the industry saw: iSCSI is able to offer about 80% the performance of 2Gb Fibre Channel," says UniSource Energy's Rima. "4Gig Fibre Channel is a little bit more, but it's not substantial enough given the cost to use it."

Rima chose iSCSI because it fulfilled his "performance needs." He runs Microsoft Exchange on iSCSI, and has been able to scale his storage up but "maintain a network topology that's low cost and low impact in terms of support."

Jim Bollinger, systems and network engineer at Washington and Lee University in Lexington, VA, has seen the same performance results as Rima. Bollinger installed Overland Storage REO disk-based appliances to back up his storage environment.

"iSCSI has been capable of doing everything we need it to do," says Bollinger. "You could take iometer.exe and take the array right up to 100Mb/sec. It's every bit as good as local SCSI and sometimes better. We've had no trouble on big files filling the pipe on our LTO-3 backup--up around 70MB/sec to 80MB/sec--and we've been backing up 7TB to 8TB a day."

10Gb/sec Ethernet
The advent of 10Gb/sec Ethernet bodes well for iSCSI. With Dynamic TCP Offload added to 10Gb/sec adapters running iSCSI, users will see the benefits--higher performance and access--of removing TCP processing from the host computer and placing it on a dedicated HBA from vendors such as Alacritech, Neterion Inc. and NetXen Inc. Dynamic TCP Offload takes advantage of Microsoft's TCP Chimney Offload technology, which offloads the TCP stack to the network card.

$2,000,000,000
According to Stamford, CT--based market research group Gartner Inc., iSCSI is expected to be a $2 billion market by 2010. In addition, IDC, Framingham, MA, estimates that from now through 2010, iSCSI SANs will show a compound annual growth rate of 74.8% for worldwide revenue vs. 4.1% for Fibre Channel. IDC also claims the iSCSI protocol will capture more than 10% of storage systems revenue and an even greater percentage of capacity by 2008.

Bollinger, who uses QLogic HBAs that perform both TCP and iSCSI offload, says he'll migrate to 10Gb/sec Ethernet for the trunks between university buildings.

"10Gb/sec to 100Gb/sec is in our planning process and further validates our decision to deploy iSCSI," says Kash at the U.S. Army Corps of Engineers. "I'm comfortable that iSCSI is going to take over from Fibre Channel, and [that] it will no longer be considered a low-cost, lower performing alternative."

Rima says "we can do TCP Offload with the TCP Offload on our NetApp boxes," adding that "10Gig should allow us to scale up quite a bit."

Besides the use of existing Ethernet switches, adapters and common Category 6 cabling, users have seen other advantages. "The ROI of iSCSI is hard to measure, but our complaints from users on performance issues are practically non-existent now," says Safeway Insurance Group's Leather. "That's a huge ROI. In our business, if someone has trouble with our Web site while they're writing insurance, they won't wait for us, they'll just go to the next insurance carrier. You can't measure the lost business."

This was first published in April 2008

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