This problem is merely an extreme case of a more general one, namely how we can assure the availability of computerised services. This problem is one of the traditional goals of computer security, the others being to assure the confidentiality and integrity of the information being processed.
Yet there is a strange mismatch between research and reality. The great majority of respectable computer security papers are on confidentiality, and almost all the rest on integrity; there are almost none of any weight on availability.
But availability is the most important of the three computer security goals. Outside the military, intelligence and diplomatic communities, almost nothing is spent on confidentiality; and the typical information systems department in civil government or industry might spend 2% of its budget on integrity, in the form of audit trails and internal auditors. However 20-40% of the budget will be spent on availability, in the form of offsite data backup and spare processing capacity.
There are many kinds of record that we may need to protect from accidental or
deliberate destruction. Preventing the powerful from rewriting history or
simply suppressing embarrassing facts is just one of our goals. Illegal
immigrants might wish to destroy government records of births and
deaths
; real estate owners might attack pollution registries;
clinicians may try to cover up malpractice by shredding medical casenotes
[Ald95]; fraudsters may `accidentally' destroy accounting information; and at a
more mundane level, many computer security systems become vulnerable if audit
trails or certificate revocation lists can be destroyed.
There is also the problem of how to ensure the longevity of digital documents. Computer media rapidly become obsolete, and the survival of many important public records has come under threat when the media on which they were recorded could no longer be read, or the software needed to interpret them could no longer be run [Rot95].
For all these reasons, we believe that there is a need for a file store with a very high degree of persistence in the face of all kinds of errors, accidents and denial of service attacks.