The networked storage project: Getting started


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Second phase-design considerations
We felt that we had adequate experience with GroupWise to do our own system design, but the SAN design was best left to those who knew FC and SAN arrays better than we did. So the SAN design was parceled out to Dell/EMC, while the GroupWise system design was kept in house (See "SAN design"). We are using EMC's ControlCenter Navisphere to monitor, provision and report on the storage systems from a Web browser.

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West Virginia University's GroupWise SAN design

West Virginia University's GroupWise 1TB e-mail SAN consists of 5 clustered post office servers--all running NetWare 6. Each post office and the SAN are dual-attached to the redundant FC switches.

For resiliency, we wanted to cluster our GroupWise Post Office Agents (POAs). In GroupWise, the POA is responsible for delivering messages to each user's mailbox. If the POA is down, all users on that Post Office are offline. The POA is also the place where user mail is held, including those storage-eating attachments. Consequently, not only was the POA critical, it also required the most storage of anything in the GroupWise system. That made it a perfect candidate for the SAN. The other elements in the GroupWise system such as the mail domains, the GroupWise Internet Access Agent (GWIA) and Web Access agents were given local storage and weren't included in the SAN.

Our next decision was whether to deploy Windows 2000 Advanced Server or NetWare as the underlying OS. GroupWise runs under either OS, so we didn't have an application issue, but we did have a SAN issue.

Although SANs are OS-agnostic, different operating systems manage clustering in different ways and that affects the SAN design. For example, Microsoft Windows 2000 Cluster Services uses a Quorum file to track the status of the cluster and applications participating in the cluster. Usually a 1GB or 2 GB partition is assigned to one RAID array for each Quorum file. The more server clusters included in the design, the more Quorum files were required. Obviously, that impacts the amount of raw data storage available on the SAN.

On the other hand, NetWare doesn't use a Quorum-like file. This results in slightly more raw storage per dollar. However, unlike Microsoft's Windows 2000, Novell's NetWare is relatively new to the clustering scene. That made it difficult for us to reach consensus on which OS we should deploy. After weighing our options, the selection team had a slight preference for NetWare. We decided to make the call for NetWare 6.x as the OS of choice.

Next, we had to determine the SAN configuration. Of course, there are several different levels of RAID that can be deployed in a SAN. Each RAID level has a different drive distribution pattern that affects both performance and redundancy.

Initially we had planned on using RAID-5, but we received a strong recommendation from a storage engineer to use RAID-10. We were told that there would be a performance advantage to RAID-10 over RAID-5. That was the upside. The downside was that the RAID-10 drive configuration would require us to increase the number of drives for the same amount of storage, and that would increase the cost. We weren't against this if it would be beneficial and wasn't overkill for an e-mail system. So we did more research.

More Information
Dell published an article on RAID level selection. The article is informative and doesn't talk about specific products. It provides a good explanation of the SAN design decision-making process.
Dell also published an article "Assessing the Reliability of RAID Systems" by Abraham Long, Jr.
An interesting, but somewhat biased comparison of RAID 5 and RAID 10 can be found here.
A list of books and articles on storage networking is available on the Storage Networking Industry Association (SNIA) Web site.

What we found discovered is that RAID-5 is optimized for disk reads and takes a performance hit primarily on writes because RAID-5 uses parity calculations to assure data integrity. This causes an extra write and read cycle in order to get the parity data on the disks. Since RAID-10 consists of multiple sets of mirrored drives, it doesn't have this overhead. Therefore, an application that's write-intensive would perform more poorly on RAID-5 than it would on RAID-10.

We measured read/write averages over a 24-hour period on three of the busiest Post Offices in our current GroupWise system. Under normal operation, there were 200 to 400 reads per second. Writes averaged only one per second. Based on the read and light write averages, we felt that we could tolerate a slight write performance hit. Therefore, we went with RAID-5.

Third phase-the implementation
While Dell and EMC were putting our order together and building equipment, we got busy with a myriad of pre-installation implementation details. The design for the GroupWise system had to be finalized and run by Novell Consulting. We needed the proper power connectors installed by our physical plant for the SAN, and the 20 GroupWise servers and then we had to implement backup power and add network connections. With the Information Systems department, we had to map out floor space for two additional racks in an already overcrowded data center. But we were underway and becoming more excited about adding a robust, fault tolerant storage solution for our e-mail system.

Web Bonus:
Online resources from SearchStorage.com: "Chat Q&A- NAS: 2002 and beyond," by Randy Kerns.

This was first published in December 2002

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