Friday, May 04, 2012

Digital Preservation: Question and Response

Question: We are trying to move away from multiple physical copies of our archival audio.  Our goal is to just have redundant digital copies and one physical copy on some medium in case of catastrophic failure with the servers. What physical medium other audio archives are using for preservation/backup copies of digital audio files.

Response: It is important to have redundant digital copies in case of failure; we have had a number of occasions where we needed to recover objects from a second or third copy when other copies failed.  There are different ways to accomplish multiple digital copies, such as copies on server, tape (LTO), cloud (DuraCloud and others), and optical discs, or a mixture. There are advantages and disadvantages with each option; we have a mixture of these, but are moving towards two options, server copies with tape backup, and M-DISCs.  We have started using the Rosetta software to manage the server copies, which will have tape copies stored in a secure off site location.  But I want an additional copy on another medium, which is our M-DISC archive.

In general optical CDs and DVDs have a short lifespan.  For a number of years, I have been caring for a large disc archive of gold CDs and DVDs; there are multiple copies for redundancy. (There are tape copies also, which have had problems as well, but the gold archival discs have been considered the preservation copies.) Multiple copies are necessary since a percentage of the discs fail each year (the percentage depends on the collection).  In order to solve that problem, two professors on campus (Information Technology, and Chemistry & Material Science) created a digital storage medium that does not fail over time and is unaffected by any normal factors, such as light, heat, cold, oxidation, pollutants, material decay, bit flips, etc.  (Extreme stress tests by the US military could not get the discs to fail.)

The university licensed the technology to a company called Millenniata which has partnered with LG and others to produce the M-DISC.  Currently the M-DISC is a DVD format, which is somewhat of a drawback if you want to store large archives, but they are developing other densities and options. (There are some organizations using a multi-terabyte Millenniata device, but I have not seen it.) I have tested and used the M-DISCs for several years and have not had any problems.  (I plan to start another round of testing on my M-DISC archive this year to check on the status of the discs; I check them for usability, read error levels, and bit transfer integrity.) So I consider this my ‘copy in case of catastrophic failure’, while the Rosetta archive is my ‘active preservation archive’. There are others in the library and on campus (digital lab, records management, etc) that use the M-DISCs for their own long term copy for images, documents, audio, video, and such. Whatever you choose, you should think about multiple copies in multiple places on multiple media.  What you choose needs to fit your circumstances and be sustainable for your program. 

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