A dynamic four-tier storage design

Finally, at tier 4, the Sun StorageTek SL500 tape library has four LTO-3 tape drives, 150 tapes, a T2000 backup server and Symantec Veritas software. This tier handles disk and tape backup, and vaulting and restoration of application and database data. Each LTO-3 drive can read and write at a sustained 80 MBps individually, with an aggregate throughput of 320 MBps. The system is modular and can be expanded in increments of 150 tapes with an additional four drives. It's currently backing up 80 TB of data per month.

Putting the pieces together

Once the components were chosen, networking details needed to be worked out, and the guiding principle was to provide connections in the right places so that client communication wouldn't be impacted by storage system operations. In the current configuration, the storage subsystems' four tiers are connected directly to one another, separate from the SAN and client FC connectivity. The tier 4 T2000 backup server has direct network connections to the tier 3 NAS Gateway cluster servers to enable backups to be done without slowing down the rest of the network. And storage, application and database expansion can be done without affecting client and storage subsystems.

The separate storage and client networks have been implemented with low-cost switch and virtual local-area network (VLAN) technologies, eliminating network contention, isolating traffic and increasing security. The backup server has its own

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direct FC and Ethernet connectivity, so backup and restores can happen around the clock. Administration of all network devices can be done via either the backup server or remotely from the administrator's desktop. And all FC connections are auto-sensed to 1 Gbps, 2 Gbps or 4 Gbps, except for the LTO-3 tape drives, which are set at 2 Gbps.

It's worth noting that software and firmware upgrades can be performed with little to no impact on other components. Firmware upgrades to the 9990V, for example, are done interactively by switching I/O and/or LUNs and connections from front to back; upgrades to the 5320 NAS Appliance are handled in a similar way. Firmware upgrades to the 6540 are also done in place, though I/O performance degrades during the upgrade. Upgrades to the T2000 backup server are done during non-backup cycles to avoid impacting the backup schedule.

The outcome

With the completed storage system upgrade in production for almost two years, the agency is able to assess how closely the initial plans mapped to actual use. There are now approximately 15,000 user accounts in the system, with daily user access peaking at around 10,000. Storage utilization is at approximately 40 TB. The agency is considering implementing thin provisioning techniques to cut down on future storage needs; even so, it's expected that the system will use about 500 TB in the next two to three years and more than 1 PB in five to seven years.

A loosely coupled system like the one the agency implemented brings with it a lot of flexibility and room for growth. But there are tradeoffs: A loosely coupled, multitiered system is inherently more complex than an integrated one from a single vendor, uses multiple management interfaces, and carries compatibility and certification path concerns. In the case of the agency that InfoPro worked with, the upfront research and engineering work made it clear that a loosely coupled system was the right choice. But each IT environment is different; a proper decision process should include not only a comparison of the available systems but discussions with vendor sales and technical reps to make sure that you fully understand their technology offerings. And it's important to dig beyond the sales pitch. Do your own research and, when needed, pull other trusted technical pros into the discussion. Taking the investigation and planning steps of the project very seriously can mean the difference between a system that's universally applauded and meets expectations -- as was the case for the multitier system detailed here -- and one that's quickly outdated or inappropriate for the project it was bought for.

BIO: Herb Ferguson is a senior systems scientist at InfoPro Corp. in Huntsville, Ala., with 25 years of IT architect, engineering, R&D, programming and network experience.

This was first published in May 2009

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