Combining storage virtualization and iSCSI

Coupling storage virtualization with iSCSI-based IP SANs provides a number of benefits.

By Mark Ferelli

Every technical advance and innovation in the storage industry comes with disruption to users’ conventional practices, battles among vendors, and the ever-present hype factor. Storage virtualization and iSCSI are no exceptions. But the hype is ephemeral and fades with time as each innovation proves its benefits and finds its applications.

Arguably, no storage innovation has inspired more uproar than virtualization. A few years ago, dozens of vendors claimed to be on the virtualization bandwagon, but today some vendors choose to avoid the “V-word” altogether.

Storage Virtualization: Technologies for Simplifying Data Storage and Management, Tom Clark’s definitive book on the subject, defines virtualization as “the logical abstraction of physical storage systems and thus, when well-implemented, [storage virtualization] hides the complexity of physical storage devices and their specific requirements from management view.” Even a basic understanding of storage virtualization enables a data-center manager to imagine the benefits: less downtime, better overall storage performance, fewer instances of lost data, the ability to aggregate LUNs, and lower costs.

The iSCSI storage systems market is expected to surge from $300 million in 2005 to more than $3 billion in 2008.
Click here to enlarge image

The catch phrase in the definition is the “well-implemented” part. Aside from any other data-center issues with virtualization, the decision must be made as to where virtualization intelligence should reside-on host servers, network switches, dedicated appliances, or in disk arrays.

Few would challenge the proposition that iSCSI is becoming an appealing alternative to Fibre Channel, with relatively low cost and easy management being the primary drivers. Like Fibre Channel, iSCSI encapsulates data and SCSI metadata (commands, status, etc.) for delivery to target devices in block format. Unlike Fibre Channel, which requires a dedicated network and specialized host bus adapters (HBAs) and switches, iSCSI can be networked over conventional TCP/IP-based Ethernet infrastructure using existing, low-cost switches-and in most cases, without specialized host adapters.

iSCSI is generally considered to be a lower-cost alternative to Fibre Channel SANs, so matching storage virtualization-which reduces costs-with iSCSI may be a sound strategy.

“A lot of the companies implementing iSCSI are new adopters of SANs and they’re using low-cost SATA arrays,” says Don Mead, vice president of marketing at FalconStor Software, an early pioneer in the IP SAN virtualization market (although the company’s IPStor software also runs in Fibre Channel environments). “Virtualization allows you to slice and dice any type of disk array, from any manufacturer, which is in line with the low-cost value proposition of iSCSI. I’d say 90% of iSCSI users are using virtualization,” he adds.

Driven by demand?

Some of the issues surrounding the combination of virtualization and iSCSI may depend on end-user demand.

Network Appliance-one of the few large vendors aggressively pushing iSCSI-made a move toward virtualization about a year ago when it revamped its file system line. The NetApp V-Series combines software and hardware that consolidate direct-attached storage (DAS), NAS, and SAN, virtualizing heterogeneous environments.

Jeff Hornung, Network Appliance’s vice president and general manager of enterprise file services, says: “We could place iSCSI targets behind the V-Series, but right now users are not demanding it. Larger enterprises have lots of Fibre Channel, and they want to virtualize across Fibre Channel arrays.” Network Appliance’s V-Series connects to and virtualizes arrays from Hitachi Data Systems, Hewlett-Packard, IBM, and Sun.

The SNIA storage virtualization taxonomy separates the objects of virtualization from location and means of execution.
Click here to enlarge image

Another issue is the relatively slow adoption of iSCSI, which can be attributed, in part, to a reluctance of some of the larger vendors to embrace the technology. Fibre Channel means high margins. And although iSCSI offers a lower-cost method of implementing SANs, in terms of both capital expenditures and ongoing “soft” costs, that translates into lower margins for vendors.

Some vendors say that iSCSI is being given short shrift on purpose. “Any time you have new technology [featuring low cost], market leaders will try to hold on to technologies and products with higher margins,” says Jim Schrand, vice president of marketing at Wasabi Systems, which sells iSCSI software (Storage Builder for iSCSI) to OEMs, integrators, and resellers.

“Some of the major vendors have done a classic “bait and switch” that has hurt sales and adoption of iSCSI,” says George Teixeira, CEO at DataCore Software. “They lure you in with the iSCSI pricing, but if you need high-level features and functions they usually force you to go to Fibre Channel.” (About half of the installations of DataCore’s SANMelody virtualization software are exclusively iSCSI.)

Where to virtualize?

As with any discussion of virtualization in the context of SANs, there is the issue of where virtualization intelligence should reside. Some vendors advocate putting the intelligence on switches, while others advocate array-based, host-based, or appliance-based approaches to storage virtualization. And since virtualization implementations are typically proprietary, users risk being locked into a given vendor’s approach.

Some vendors contend that virtualization belongs in the storage array, arguing that although switch-based virtualization allows users to choose almost any vendor’s disk arrays, users have no choice in switches when they need to scale.

“Some say that switch-based virtualization is not good for iSCSI because it becomes another management point,” says Eric Schott, director of product marketing at EqualLogic, which sells IP SANs and iSCSI disk arrays. “Switch-based virtualization is a vendor tactic that forces customers to upgrade all their switches and move to proprietary switching.” Schott also argues that popular features such as snapshots and replication are less efficient in switch-based virtualization devices. (EqualLogic’s iSCSI disk arrays include virtualization on the controllers.)

Some vendors are covering all the bases. For example, FalconStor’s IPStor can run on a dedicated appliance (Linux or Solaris server), in intelligent switches such as Cisco’s MDS 9000 series via SANTap Service, or in an IPStor server with disks (essentially, array-based virtualization).

Steve Malan, chief storage architect at Wasabi, asserts that “iSCSI is storage virtualization.” Where people get confused, he suggests, is in mistaking virtualization for the effects of virtualization. “Virtualization is everywhere-PCs, servers, storage. The Holy Grail will come when users don’t need to worry about complexity,” says Malan.

The need for speed

Typically, block-based SAN applications are I/O-intensive. Content-rich applications such as video/audio streaming, voice over IP (VoIP), etc., load systems even further.

As such, some IP SAN environments may require IP/iSCSI acceleration cards, which offload network processing to dedicated host adapters without changes to applications. Vendors such as Alacritech, Chelsio, Intel, QLogic, Neterion, SBE, and Silverback sell acceleration cards with iSCSI and TCP/IP offload engines (TOEs) for IP SAN environments that need the utmost in performance. Some of the accelerators are available with support for 10Gbps Ethernet (10GbE).

In addition to accelerator cards, the advent of 10Gbps Ethernet may ease the performance challenge associated with iSCSI-based SANs.

LeftHand Networks’ Karl Chen, vice president of marketing and business development, says: “10GbE will accelerate adoption of iSCSI. In the labs, 10GbE is showing great performance over many more servers.” However, all vendors agree that pricing for 10Gbps Ethernet will have to come down significantly before the technology causes an appreciable increase in iSCSI SAN adoption.

Some vendors argue that even today, with Gigabit Ethernet, it’s possible to design an iSCSI-based IP SAN that rivals the performance of a Fibre Channel SAN. SBE, for example, reports “on par” performance between Fibre Channel and iSCSI in tests using two Gigabit Ethernet ports versus one 2Gbps Fibre Channel port, according to Leo Fang, vice president of engineering at SBE, which makes iSCSI target and initiator software. And those tests were conducted without iSCSI accelerator cards.

With accelerator cards and the advent of affordable 10Gbps Ethernet, iSCSI could move beyond its mostly Windows-based roots into enterprise-level Linux and Unix environments.

“From a cost perspective, 10Gbps Ethernet is in line with high-end Fibre Channel SANs if you factor in switches and HBAs,” says David Clark, director of technical marketing and product engineering at iStor Networks.

“The performance of iSCSI over Gigabit Ethernet is on par with Fibre Channel today, and 10Gbps Ethernet will eclipse Fibre Channel’s performance, enabling iSCSI to move from SMBs [small to medium-sized businesses] to the enterprise. In addition, you have the distance advantages of iSCSI.”

iStor sells ASICs and the GigaStor line of subsystem controllers for iSCSI storage systems. The GigaStorATX controllers are available in 1Gbps or 10Gbps versions. In early tests of the 10Gbps Giga-Stor controller, iStor clocked more than 1,150MBps, according to Clark.

As iSCSI moves into enterprise environments, virtualization will no doubt become a part of the expected set of requirements for IP SANs. Virtualization simplifies complex storage environments, and simplification is one of iSCSI’s calling cards.

“iSCSI attracts users that have never built a SAN before, many of which come from DAS environments,” says Zophar Sante, vice president for market development at Sanrad, a vendor of multi-protocol (including iSCSI) switches. “But to create utility storage for tens or thousands of servers, a robust iSCSI feature set is required. iSCSI makes it cheap, and virtualization makes it easy.”

(Note: For more information on how and why end users are using iSCSI-based IP SANs, see “Why users are embracing iSCSI SANs,” InfoStor, January 2006, p. 30. Our May issue will also include a series of iSCSI case studies.)

Mark Ferelli is a freelance writer specializing in storage. He can be reached at mcferelli@yahoo.com.

CASE STUDY: JA moves from DAS to iSCSI SAN

Since 1919, Junior Achievement (JA) has been dedicated to educating young people about business, economics, and free enterprise. The Colorado Springs-based JA office supports approximately 142 operations in the US and in 98 countries around the world.

Recently, JA’s IT management made the decision to move from its limited direct-attached storage (DAS) implementation to an enterprise-class storage network. The decision was in part driven by downtime problems impacting about 2,700 remote users. George Murphy, Junior Achievement’s senior director of network services, says that the original plan was to deploy a Fibre Channel SAN, funded by donor contributions. But JA instead opted for an IP SAN, partly because of its lower cost.

Murphy now has three NSM 200 storage devices and SAN/iQ 6.3 software from LeftHand Networks in a 6TB cluster serving remote users. “The data is always there, it works with my SQL database, and I don’t have to hire a consultant to run my IP SAN as I would have {had to do] with a Fibre Channel SAN,” he says.

Installation of the IP SAN was simple: “We installed iSCSI and migrated our file servers to it. Within three days, we had our Exchange servers up and running,” says Murphy. He estimates that a Fibre Channel SAN would have taken weeks to deploy and could have cost hundreds of thousands of dollars more-a key factor since Junior Achievement is a non-profit organization.

Finally, Murphy had to consider scalability. “We anticipate outgrowing our current cluster, but the IP SAN will let us grow as much as we want to.” JA plans to add as much as 10TB in the foreseeable future.
-Mark Ferelli

This article was originally published on March 01, 2006