Magnetic tape to the rescue

Univac magnetic tape (Photo credit: Marcin Wichary)

Information storage: A 60-year-old technology offers a solution to a modern problem—how to store all those bits and bytes cheaply and reliably

WHEN physicists switch on the Large Hadron Collider (LHC), between three and six gigabytes of data spew out of it every second. That is, admittedly, an extreme example. But the flow of data from smaller sources than CERN, the European particle-research organisation outside Geneva that runs the LHC, is also growing inexorably. At the moment it is doubling every two years. These data need to be stored. The need for mass storage is reviving a technology which, only a few years ago, seemed destined for the scrapheap: magnetic tape.

Tape is the oldest computer storage medium still in use. It was first put to work on a UNIVAC computer in 1951. But although tape sales have been falling since 2008 and dropped by 14% in 2012, according to the Santa Clara Consulting Group, tape’s decline has now gone into reverse: sales grew by 1% in the last quarter of 2012 and a 3% rise is expected this year.

Alberto Pace, head of data and storage at CERN, says that tape has four advantages over hard disks for the long-term preservation of data. The first is speed. Although it takes about 40 seconds for an archive robot to select the right tape and put it in a reader, once it has loaded, extracting data from that tape is about four times as fast as reading from a hard disk.

The second advantage is reliability. When a tape snaps, it can be spliced back together. The loss is rarely more than a few hundred megabytes—a bagatelle in information-technology circles. When a terabyte hard disk fails, by contrast, all the data on it may be lost. The consequence at CERN, specifically, is that a few hundred megabytes of its 100-petabyte tape repository are, on average, lost every year. Of the 50 petabytes of data held on hard disk, however, it loses a few hundred terabytes in the same period.

The third benefit of tapes is that they do not need power to preserve data held on them. Stopping a disk rotating by temporarily turning off the juice—a process called power cycling—increases the likelihood that it will fail. The fourth benefit is security. If a hacker with a grudge managed to break into CERN’s data centre, he could delete all 50 petabytes of the disk-based data in minutes. To delete the same amount from the organisation’s tapes would take years.

Tape has two other benefits, as Evangelos Eleftheriou, manager of storage technologies at IBM’s research laboratory in Zurich, points out. It is cheaper than disks (a gigabyte of disk storage costs 10 cents, versus 4 cents for tape), and it lasts longer. Tapes can still be read reliably after three decades, against five years for disks.

Tape will never be the whole answer to storing data, according to Dr Eleftheriou. But it forms a crucial part of a “storage hierarchy”.

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