When a user requests data from tape, the disk is used to provide a portion of the relevant data immediately, while the system seeks the rest of the relevant material from the tape.
"It masks how long it takes to seek that data on tape," said Toigo, founder of Toigo Partners International, a disaster recovery consulting firm.
He said data that is archival shouldn't be on disk anyway, plus long-block files like video and telemetry are able to better take advantage of the linear structure of tape. "This is a very low-cost solution," he said, and noted that such an approach saves energy.
While smaller files don't work well with tape, Toigo said some vendors are looking at ways to change that. He pointed to Spectra Logic from Black Pearl, which uses a method that essentially groups small files together to represent them as objects.
"All of a sudden, you have a file system in a file system -- you can dump that to tape," said Toigo of that approach.