Massive storage failures
Basically no matter how much money you spend on the system housing your data there are still many ways in which it can fall over and create opportunities for data to be lost. This may be from hardware/software failure or an act of war. The longer you try to store data the more likely this will occur.Mistaken erasure
Sometimes people accidentally delete things and if it's the only copy, then it's gone. On the other hand sometimes people think that they no longer need a piece of data and delete it on purpose only to find that it was in fact useful. The longer you try to store data the more likely this will occur.Bit rot
No affordable digital storage is completely reliable over a long period of time. For example some CD's have recently been shown to have a life span of only 2 years which could cause significant problems for anyone relying on them. Other media such as magnetic tape also suffers various types of bit rot. The worse thing about this threat is that is often undetected until it's too late to recover the material. You would very nearly have to employ someone to check all your media all the time to minimise data losses which would make most of these mediums too expensive to seriously consider in a preservation project. Bit rot is inevitable with any storage medium over a period of time.Outdated media
Over time all kinds of digital media become outdated. Technology is driven by innovation which unfortunately leads to very short periods of relevancy before redundancy. Data stored on redundant media becomes effectively useless if the appropriate hardware is not available to read it. This is a particularly difficult issue to manage where data is stored over long periods of time. Ideally, long term data storage should be technology independent, however this is not practical. A Cornell University website (mentioned above in another post) has actually documented the lifespan of various storage media with floppy disks lasting a whopping five years.Outdated formats, applications and systems
As hardware becomes redundant, so do file formats and the software which interprets them. A good example of this is Word Perfect
; try to find a computer today which can read a Word Perfect
Fortunately, system and format redundancy does not usually happen at quite as rapid a pace as hardware.
This is a difficult problem for long term storage and there are two common, but awkward, solutions. The first is to preserve a copy of the appropriate software and make it available wherever that data is stored. This becomes increasingly unmanageable as the types of systems required increases. The second is to migrate data to an acceptable format, for example all text files might be migrated to pdf thus only requiring copies of Adobe Acrobat to be preseved. However, during the migration process it is possible to lose data. It is also a costly process in terms of work hours and expertise.Loss of context
Some data can be related, and this relationship can be vital to data interpretation. A good example of this might be the Rosetta Stone, discovered in Rashid, Egypt. The stone is engraved with hieroglyphics in three different languages and without the "key" of what these symbols meant noone was able to read the inscription. It took a French scholar Jean François Champollion fourteen years to decipher the inscription. Can you imagine if you had to take that amount of time to decipher each document on your PC because someone had forgotten to preserve the relationship between that document and its key? It would be like trying to assemble Ikea furniture without instructions, a complete waste of time. Unfortunately, if this relationship is not identified and preserved when information is first stored it is unlikely to ever be recovered. The longer the data is kept without this relationship, the less likely it is to ever be resolved.Intentional attacks
Unfortunately in the world we live in there are some people who intentionally destroy or damage digital assets for a variety of reasons. As much of the information is currently located in open access repositories accessible via the internet it is also vulnerable to attack. This is a threat to both long and short term storage.Lack of resources
Many institutions simply do not have the resources, usually financial, to consider digital preservation. These strategies are often overlooked as low priority and are likely to remain so until a major data loss scares people into action.Organisational failure
This is a massive threat to long term digital storage of any kind. Technology is so dynamic not only in innovations but also movement with vendors and competition killing off what seemed to be at one point very strong tech players. For this reason it would be a folly to rely too heavily on any one vendor/system/sponsoring organisation because they change and often change quickly. Digital assets which need to be preserved long term must be protected from the failure of any one organisation. Unfortunately this is easily said but hard to plan for in such a dynamic environment.
Why Traditional Storage Systems Don't Help Us Save Stuff Forever
Baker, M. Keeton, K. Martin, S. June 27 2005
HP Labratories Palo Alto