More sophisticated archives make extensive use of metadata and document retrieval systems which have been developed for digital libraries and the like. Each archived disk needs a full and structured list of contents stored on it in an accessible format such as UTF-8 text, and a printed summary should be stored with the disk to save you from having to mount disks in turn to look for documents on them. Even when structured rigorously, finding individual documents can be extremely frustrating. Looking through archives only a few months later can be a salutory experience. Avoid any form of compression, which can amplify the effects of bit rot, making it impossible to extract even plain text files. Consider tarring (using tar, pax or cpio) smaller files together if necessary. ![]() Tens of thousands of files should write in an acceptable period, but many more than a hundred thousand may not be practical. Video, audio and rich media should use widely-used compressors which are likely to remain available in the future.īeware when trying to store very large numbers of files to a single Blu-ray disk. PDF provided that it complies with one of the archival standards PDF/A-1 to /A-3.Standards which are likely to be reliable during our lifetimes at least include: The best compromise in an archive is to keep at least two different versions of each document, one in its original format, or exported into a format which can be accessed by other apps too, and one in a more enduring format even if that limits access to its components. Proprietary and binary file formats are notoriously short-lived, but invaluable when you want to access the contents of complex documents. These are significantly more expensive, have much lower adoption rates and are dependent on hardware and software which may not prove as enduring as plain Blu-ray. There are also some specialist products for the archiving market such as Sony’s Optical Disk Archive, offering write-once storage of up to 5.5 TB in an eleven-disk cartridge, and Blu-ray based Archival Disk which may reach 1 TB on a single disk. My previous experience with optical drives is that there’s a sweet spot for each writer and type of disk which is the best compromise between performance and reliability. Opinions are mixed as to the optimal burn speed: some advocate using the slowest possible, down to 1x, but apart from making each burn much longer, you’re probably best off using the rated speed of the disks. ![]() If any fails the verification step, discard that disk and burn another. To do the job thoroughly, you should burn two copies of everything you intend to archive and verify them. As no Mac has ever come with a built-in Blu-ray writer, and none now supports internal optical drives at all, there’s a wide choice of external models available. M-DISC has become a popular choice among those seeking greater longevity, and has both theory and manufacturers’ claims to support that, but many Blu-ray writers still don’t support burning M-DISCs, and you’ll need to choose yours with care. Matching the writer drive specification with media isn’t alway easy. Some manufacturers quote one hundred or one thousand years ‘archival life’, which assumes that, over the long term, the disks age as expected from accelerated ageing tests, and that they remain stored in optimal conditions for the whole of that period. You should also be extremely sceptical about claims of their longevity. ![]() Blu-ray can readily cope with 50 or 100 GB on each disk, but those disks aren’t cheap: ‘archival quality’ BD-R disks typically cost around $/€/£ 5-10 each. ![]() Although DVDs have been very widely used, their capacity is generally too low for modern use. Currently the best bet is some form of optical disk, either DVD or Blu-ray. There’s simply no equivalent electronic storage medium which can offer high-density and proven permanence. Traditional historical archives consist almost entirely of documents printed and written in ink on paper. It’s one of the most difficult problems in computing, and one which most of us have yet to tackle seriously. But where are you going to store them ‘in a safe place’ for the future?Īrchiving is about moving old documents and records from current storage to somewhere more permanent, which frees up active disks and ensures long-term access to those files in ten, fifty or even five hundred years. We tend to think of electronic records as being contemporary and recent past. Yet it’s extremely unusual to find computer files which were created before 1990, apart from those with ‘null’ creation dates of 1 January 1970. Most of us have birth certificates and other documents, perhaps even from our ancestors, which go back fifty years or more.
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