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How the NERSC Gets More Bang for Its Buck with Tape Storage

by on January 20, 2011

Not a day goes by without some critic of tape storage declaring its imminent demise, so it’s refreshing to see an organization that actually embraces the technology as a robust business tool. That’s how the National Energy Research Scientific Computing Center (NERSC), in Berkeley, Calif., looks at the medium.

DLT_tape_colors For the agency, which is managed by the Lawrence Berkeley National Laboratory, of the U.S. Department of Energy, tape is more than a necessary evil. It is an active part of the organization’s storage infrastructure.

The agency is attracted to tape for all the benefits typically cited by the medium’s fans. It’s reliable and cheap. Over a one year period, the agency recently upgraded its data archives of some 13 petabytes (13,000 terabytes) from an older to a newer tape technology.

The older data was stored on almost 24,000 cartridges–32 percent of them up to 12 years old, 38 percent up to eight years old and 30 percent up to two years old. Only 13 tapes contained information that couldn’t be read, or more than 99.9 percent of the tapes were 100 percent readable. Of the 13 tapes that contained corrupted data, only 14 files had issues. And most of those files could be read. They just contained blocks of data—in the 250MB to 500MB range—–that was corrupted. The total amount of data lost in the transfer was about 100GB.

As for cost, the agency estimates that on a dollar-per-gigabyte basis, tape storage is five percent that of disk storage.

Those benefits, though, are just half the story. The agency uses its tape archives aggressively. While the I/O activity level in a typical enterprise tape archive is only five percent reads, the activity level for NERSC’s archive is 30 to 40 percent reads.

“It sees tape as an investment and not just a cost and uses its tape as a dynamic part of its [entire] IO infrastructure rather than as a collection bin,” the Enterprise Strategy Group noted in a case study of the agency.

“[I]t has made a straightforward cost-benefit business decision based on providing optimum efficiency to its users,” the group added. “And in so doing, it has debunked the ideas that tape is inherently unreliable and that disk and tape share similar long term TCOs [Total Cost of Ownership].”

Obviously, we at B&L have a bias toward tape backup because of the tape management systems we offer. but what do you think? What does your company use for long-term storage of data?

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