Digital preservation is realized in this invention by providing a method and system for long term error-free storage, having means for requested files to be retrieved error-free from the storage, and having means for interpretation of the retrieved files, for all the time span that the storage continues on. User-requested files, when retrieved from the long term error-free digital storage, are retrieved without possibility of corruption of the files of the storage. The storage of the files is continued on in time, by being forward copied, error-free, from one-era storage media to next-era storage media. Planning for the timing of forward copy from the one-era media is accomplished by methods for contemporaneous determination of the actual lifetime of the one-era media, through monitoring scans of the written-to media.