SAN technology considerations for data center virtualization

While storage area networks (SANs) are key in a virtualization rollout, one company found that problems can arise when an initial SAN deployment isn't properly planned.

This is one of three case studies on the merits of server virtualization in the data center. Others detail improving IT efficiency with server virtualization and implementing virtualization software during a server refresh.

Storage area networks (SANs) have become a staple in many modern data centers, especially those that use server virtualization technologies. SANs meet the storage capacity requirements for today's demanding applications and ensure the stable and reliable application performance needed to keep users productive.                                                  

Choosing a SAN, however, is only the first step to obtaining the best storage for your data center. When rolling out SAN technology, you must know how to invest in sufficient capacity, plan the best utilization, use the right management tools and ensure proper integration into the existing environment. Unfortunately, these additional SAN technology considerations are often overlooked until after a SAN deployment, causing an entirely new set of challenges and expenses.

SAN technology is used in one data center virtualization rollout
"We supported the implementation of a virtualization project with an architectural firm in Cleveland," said John J. Ford, principal at Ford Associates, an IT solution provider located in Akron, Ohio.

The project involved virtualizing seven servers, and adding about 4 TB of storage for all of the virtual images, excluding data protection storage. Using a SAN would meet the needs for storage and performance, and Ford recommended a Dell EqualLogic SAN appliance under iSCSI.

"[As a preferred vendor] having a Dell server environment was a strong point for the EqualLogic box," Ford said. He also noted that the initial SAN installation took about a day, but migrating their client's servers onto virtual machines (VMs), getting them onto the SAN and then having them tested took several weeks.

The project consolidated the client's seven physical servers to three, with six VMs across two Dell 2950 servers (the file server remained unvirtualized on a third server).

SAN technology issues beyond the initial deployment
Ford explained that while his customer's EqualLogic SAN subsystem installed and configured quickly and easily, the client had to contend with business continuity considerations for the SAN data.

"The virtualization was the easy part, but there were challenges with the storage requirements after the implementation," Ford said. The client was not ready to commit the financial resources needed to address those subsequent issues.

"The costs they didn't see going into it were the licensing costs and replication costs," according to Ford.

There were several commonly accepted options that could address the storage requirements: replicate the EqualLogic SAN at an off-site data center, use a SAN backup solution or develop a compatible SAN that could receive replicated data. These hardware, software and procedural implications were an unexpected roadblock for the client.

The client also failed to budget for their VMware management tools, which would properly manage the virtual environment. Shifting to the VMware platform imposed another unexpected change to the client's power control scheme. UPS systems communicating with servers via USB/serial interfaces became incompatible with VMware. This imposed yet another unplanned wrinkle that required some re-architecting to correct.

Virtualization works, but plan ahead with SANs
Ultimately, the move to virtualization was beneficial for the client. Ford points out that the daily operations realized very little direct change -- everything was running the same way. The payoff came with the inclusion of failover, high availability and vMotion features, combined with the availability of ample SAN storage, which made it possible to increase the size of mail stores. These enhancements improved email server uptime dramatically and supported maintenance activities that wouldn’t be possible in a non-virtualized environment.

Ford emphasized that prospective virtualization and SAN adopters must think ahead regarding the costs and requirements that occur beyond the initial SAN technology deployment.

"For an initial SAN deployment, most people make good decisions for their environments, but the issues [presented with] backup and replication are sometimes ignored or aren’t dealt with," Ford said.

Stephen J. Bigelow, a senior technology writer in the Data Center and Virtualization Media Group at TechTarget, has more than 15 years of technical writing experience in the PC/technology industry. He holds a bachelor of science in electrical engineering, along with CompTIA A+, Network+, Security+ and Server+ certifications, and has written hundreds of articles and more than 15 feature books on computer troubleshooting, including Bigelow’s PC Hardware Desk Reference and Bigelow’s PC Hardware Annoyances.

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