Rapport

FFI-RAPPORT 16/00707

the HDD – the average lifespan is six years – and the high failure rates, it is common to make

use of several disks, known as RAID (redundant array of independent disks), in order to ensure

data redundancy and minimise the risk of data loss [60, 57].

10.1.2

Optical disk (CD)

Optical disks (CD) are flat circular disks that encode digital data on one of its flat surfaces [57].

An optical disk drive uses a laser light to write data onto or read data from an optical disc,

which includes CDs, DVDs and Blu-ray disks [61]. One version of the medium – CD-R or

DVD-R – writes the information onto the CD or DVD only once but enables the information to

be re-read many times, whereas another type – CD-RW or DVD-RW – allows new information

to be rewritten onto the same medium. If the former is used, the data is immune to corruption

for the longevity of the medium. Optical disks are cheap and easy to use and are most

commonly used for distribution and storing of published software and games, as well as audio

and video recordings [62].

Compared to other storage devices, optical disks offer low data capacity with a maximum of

700 megabytes (MB) for CDs, 8,4 gigabytes (GB) for DVDs and 50 GB for Blu-ray [63]. Their

lifespan varies depending on whether they are recorded or not: the lifespan of an unrecorded CD

is 5-10 years, whereas the lifespan of one with content is 2-5 years [64]. These features illustrate

how optical disks were not originally developed for long-term preservation, but rather as a mass

consumer product. Making use of optical disks in a digital archive requires a significant

investment in knowledge and technology, which is why they are better suited as a digital storage

technology used for a limited period of time. They are not a permanent solution, as both future

developments in technology and the deterioration of the optical disk over time will necessitate

the migration of the disk’s content onto a new medium. CDs and DVDs are fragile and may

snap or scratch easily, in addition to being affected by environmental factors such as dust, heat

and UV light [57, 62].

10.1.3

Magnetic tape (LTO)

Magnetic tape is an analogue medium for magnetic recording, made of a thin magnetisable

coating on a long, narrow strip of plastic film. The magnetic coating makes it possible to retain

electronically encrypted data in digital format [57]. They use serial access to find a piece of

data, which makes it fairly time-consuming to find and retrieve data. Therefore, it is most

appropriate to use magnetic tapes for storage of data that is not likely to be needed instantly.

Another disadvantage is that the data on the magnetic tape may be corrupted if the tape is placed

near a strong magnetic field, e.g. a large speaker or a magnet.

Magnetic tapes can store up to six TB of uncompressed data [65]. Their lifespan is up to 30

years under optimal storage and handling conditions, but this really only applies when the store-

and-ignore principle is put to use, i.e. that the digital data is transferred to the medium and then

hardly accessed again. When one includes the added wear and tear of a magnetic tape that is in

use, a more realistic lifespan is about 10-20 years. Still, due to the delicacy of the material,