Data may have to be stored for long periods of time for various reasons, not least because it may be required as evidence many years later (e.g. In Ireland it is required that all invoices be kept for a period of seven years) or because the Revenue Commisioners and auditors demand access to data for a long period. There can be a few basic rules of data management more often broken than the one about keeping several back-up copies, in different locations of all sensitive data. But trade data exchanged by EDI must always be regularly backed up - your companies very existence may depend on it. Magnetic media can be vunerable and it may be well worthwhile to invest in an optical disk drive, which has the additional benefit from an auditing point of view that data once written to it cannot later be ammended.