Block virtualization: Switches, appliances, arrays

By Kevin Komiega

It seems as if the argument over where block-level virtualization should reside has been around since the dawn of SANs. Should it run on a switch or in the array, or should virtualization and all of the management and data services it brings with it sit on an out-of-the-way appliance somewhere on the network? The answer is: It depends on your specific requirements.


Each use case is unique, and an approach that fits one data center does not necessarily work in another. However, regardless of where the technology is implemented, block-level virtualization is delivering as promised, according to end users, as shown in the following case studies.

Switch-based virtualization

Vadim Kogan, a programmer and analyst at the University of California, Berkeley, is part of an IT team that supports UC Berkeley’s IT infrastructure for the electrical engineering and computer sciences departments. As such, managing storage requirements for approximately 1,500 end users falls under his purview.

Kogan’s group deals with three common storage events. First is the provisioning of home directories, and the second is providing project space or self-contained capacity for research and development projects. Lastly, the team is responsible for the centralized management of storage for UC Berkeley’s mail servers.

When combined, these are not simple tasks, but they are manageable using storage virtualization technology. “I deal with a lot of things, including taking care of all of our back-end storage needs,” says Kogan, “but give me the proper technology and things can be done very efficiently from a management perspective.”

Kogan decided to implement virtualization on a fabric switch. It was a decision based largely on the existence of legacy hardware. Kogan was already running a Cisco MDS 9000 Series SAN switch—a factor that weighed heavily on the institution’s choice of virtualization solution and one that eventually narrowed potential vendors/products down to two: Incipient’s Network Storage Platform (iNSP) software or EMC’s Invista, both of which provide storage virtualization using the MDS switches.

“On one hand, we had to weigh the existence of the Cisco MDS switch, which is very big and very expensive, but on the other hand I liked the concept of virtualization on a switch in general because you have the expectation that things will operate more or less at wire speed, and you can zone things properly for critical tasks,” says Kogan.

Kogan says that EMC’s Invista and Incipient’s iNSP were likely to offer similar functionality and performance, but in the end the decision to buy Incipient’s virtualization platform was one of cost, support, and interoperability.

“One of the key features for me is Incipient’s ability to support multiple vendors on the back-end,” explains Kogan. “If I were to opt for virtualization from Hitachi or Sun, for example, they can do the virtualization and they can support a few large enterprise storage systems as well, but are they going to support a new, small-scale disk shelf that came out from IBM?”

Incipient’s iNSP is software that uses Cisco MDS 9000 switches to bring non-disruptive online data migration, network volume management, storage provisioning, and copy services to the storage fabric. The software resides on Cisco’s MDS Storage Services Modules (SSMs) housed within an MDS chassis and delivers a common suite of storage services across a SAN environment to applications and hosts.

Choosing to implement virtualization also leaves the door open for more advanced storage services in the future, according to Kogan. He says the ease of management and ability to copy and move data are reason enough to invest in virtualization, but adding features without replacing hardware presents other opportunities for change in the data center.

“You don’t just get a virtualization platform. You get the possibility of doing other things in the future at wire speeds. I suspect that approach will appeal to more customers because of the promise of advanced data services,” says Kogan.

Appliance-based virtualization

Chances are that somewhere in your house, you have a can of WD-40 waiting to fix that next hinge or rusty mechanism, but inside WD-40, the company, the squeaky wheel that needed attention was the company’s e-mail system.

“Our e-mail solution wasn’t redundant. There was no disaster recovery at all. We faced days of downtime when there was a problem,” says Jennifer Duke, a collaboration systems engineer at WD-40. “We didn’t realize how important e-mail was until we were down for three days. That was the driving force for going forward with storage virtualization.”

Duke, whose responsibilities include maintaining the company’s SAN infrastructure, e-mail, and communications systems, embarked upon simultaneous implementations of Microsoft Exchange and appliance-based storage virtualization technology from LSI StoreAge.

WD-40’s IT infrastructure is based on a dual fabric with four 2Gbps Fibre Channel switches from QLogic, a pair of 3TB TotalStorage DS4000 Fibre Channel disk arrays from IBM, and two LSI StoreAge Storage Virtualization Manager (SVM) appliances.

The SVM is a SAN appliance that provides virtual volume management in heterogeneous environments. The SVM features storage capacity and storage performance pooling across the entire SAN domain. Designed to virtualize storage off the data path, the StoreAge SVM does not impose performance penalties and provides centralized management for applications such as remote mirroring, snapshots, and other business continuity applications.

WD-40’s buying decision was based on a number of factors, but avoiding vendor lock-in was at the top of the company’s list.

“We looked at [virtualization] products from IBM, EMC, and Hewlett-Packard, but we did not think they would have given us the broad flexibility we needed for growth,” says Duke. “The SVM has the ability to provide redundancy without having to have a specific vendor’s storage. We can have two different boxes, and that was a huge bonus for us and a driving factor for the purchase.”

Using the virtualization appliance, WD-40 was able to meet its data recovery needs and is using virtualization for Exchange and file serving and will soon incorporate e-mail archiving into the mix.

“The ease of use and ability to do point-in-time copies were huge factors for us. The ability to recover is so much faster now than if we would have had to attempt to recover from backup tapes,” says Duke.

There was one minor hiccup during the implementation. WD-40 made a decision at the beginning of the project to go with SATA drives versus high-speed Fibre Channel drives, and the decision created some performance issues for some applications.

“We ran into problems running some advanced features like synchronous mirroring,” says Duke. “It was not an issue with the SVMs; it was the drives. In hindsight we know that buying higher-end, high-performance Fibre Channel drives just works better.”

Array-based virtualization

Like many municipalities, the City of Westerville, OH, has a sprawling infrastructure. The city’s IT gear is spread across 15 locations, with a concentration of 32 servers and a Xiotech Magnitude 3D 3000 Series SAN array at a central operations center.

The virtualization technology inherent to the Magnitude 3D gave Westerville’s IT team—which includes three administrators—simple storage management beyond their expectations.

“The base package gave us all the features we needed. The management capabilities and virtualization are already there. Some vendors offer those features as options or extra hardware pieces. That can get expensive for a small to medium-sized government entity,” says Bryan Mundy, network operations manager for the City of Westerville.

Provisioning storage for new servers went from being a time-intensive process to a simple, wizard-driven task. “We no longer have to manage each spindle. We see a big box with a set amount of space. That allows us to create a LUN, assign the space, and attach a server to it,” says Mundy.

The Xiotech SAN serves data for the majority of Westerville’s Web services applications, including the city’s Website and “e-government” services.

Mundy says that his paramount concern was to find a cost-effective storage system that was easy to manage.

Mundy’s SAN is attached to approximately 15 of Westerville’s servers, including IBM BladeCenter systems running Microsoft SQL Server clusters, Novell NetWare and more, all of which now boot directly from the SAN.

Another benefit of the SAN’s virtualization technology is the ability to add capacity on-the-fly without bringing down the array. The Magnitude 3D array is licensed for 3.6TB of capacity, but the city will be upgrading the SAN soon to accommodate capacity growth. The plan is to grow the SAN to 5TB by next year and add another 3TB in the future.

According to Mundy, adding capacity would be a hassle without virtualization. “The virtualization technology also lets you add an extra set of disk drives while the system is running, and you can take existing volumes and copy them across the new space,” he says.

This article was originally published on April 01, 2008