Re: Archival fixed storage media

[Tim Au Yeung]

Marla (and others), The CLIR resource is an excellent resource once you’ve made the decision to use CD-R/Ws/DVD+/-R/Ws as your archival storage format. It actually gives a very good overview of the optical media technology.   While I’ve dealt with the issues of CD-R technology and particularly the dyes elsewhere, discussions of network storage vs. removable media and the newly bantered about “2 year” longevity of CD-Rs sparked my response.   There really hasn’t been a significant amount of hard science applied to the longevity of writable media. I’m familiar with one longevity study that the Library of Congress is engaged in on the longevity of CD-ROMs but not with locally written media. Part of the problem is the methodology applied to developing measures of longevity. We really don’t have good ways of measure the effects of time on optical media and the ability to test the quality of CD media traditionally has required expensive, specialized testing equipment usually in labs. There is software out there now for some quality testing using a conventional reader (like http://www.cdspeed2000.com/) but of course, it still requires someone who is fairly knowledgeable to make use of the software.   When considering an archival media format, I think it’s important to recognize that there are two principles at play with archiving digital files:   Risk reduction Active management   Risk reduction encompasses many of the traditional environmental considerations such as storage environment and enclosures, humidity, temperature, etc. It also encompasses the inherent properties of a media format for long term stability. Active management, on the other hand, involves the steps to continually assure that the digital files are available and intact on the media, including refreshing and periodic checksum tests. The choice of media should reflect considering both principles.   Rather than dealing with the whole spectrum of media, I’m going to focus on magnetic hard disk media and optical removable media. While there are distinctions between CD and DVD formats, I think they are more alike than not and can be considered together.   In terms of risk reduction:   Optical Media Pros: -          sensitivity to environment minimal -          write-once versions available to ensure no overwriting or accidental changes Cons: -          longevity unknown -          subject to physical damage   Hard Disk Media Pros: -          great capacity -          allows for continuous tests of viability Cons: -          sensitive to the environment, particularly ambient magnetic fields -          can be overwritten or accidentally erased     In terms of active management Optical Media Pros: -          wide variety of read and write devices -          inexpensive (~CDN $0.75 / GB) -          easy to create multiple copies Cons: -          capacity is relatively small making management more difficult (greater handling) -          write-once nature an impediment to an active management of individual files -          requires more physical organization   Hard Disk Media Pros: -          large capacity makes managing easier -          always active nature allows continuous error checking Cons: -          adding capacity not always straightforward -          more expensive (CDN $1.25 / GB for the hard disk, CDN $4-6 / GB for a NAS solution) -          requires more technical infrastructure   In an ideal world, you’d have a NAS/SAN-based system for an online copy of a master file that is regularly checked for integrity with a CD/DVD copy offline in a separate location that is periodically spot checked and replaced every 4-5 years from the NAS/SAN-based copy. Obviously, it requires a fairly large organization to organize a system like that and given the costs, two copies on optical media may be the practical choice.   What I would see as a practice that would lead to greater loss is to choose less than optimal technical standards for the digital files (resolution, bit-depth, lossy compression, etc.)  to try to conform to the existing storage infrastructure. Better to get all the quality you can in the files and settle for a more cost effective solution for storing them even if there is uncertainty at this point.   --------------------------------- Tim Au Yeung Manager, Digital Object Repository Technologies Information Resources University of Calgary   -----Original Message----- From: Richard Urban [mailto:museumn...@earthlink.net] Sent: Tuesday, November 18, 2003 3:14 PM To: mcn-l@mcn.edu Subject: Re: Archival fixed storage media   Hi Marla!   After replying to a similar comment on the Imagelib list I learned of a great new resource that CLIR has just made available "Care and Handling of CDs and DVDs: A Guide for Librarians and Archivists" http://www.clir.org/pubs/reports/pub121/pub121.pdf   One of my big concerns are the reports on incompatability between the different types of DVD encoding (DVD-R, DVD+R, DVD-RW. DVD+RW, etc.) and hardware used to read it.  The CLIR document doesn't go too deeply into this issue but industry surveys have indicated that the theory that readers are interoperable isn't necessarily reality.    Any other information about this issue would be appreciated.   Many CDP projects are smaller institutions that don't have the staff or budgets to maintain large online storage systems so our recommendatations still lean towards gold CDs.  However for the project as a whole we have moved torwards network attached storage (NAS) that allows us to expand as needed (similar to Matt's suggestion).  CDP participants who have the infrastructure to support it are also moving in this direction.  -----Original Message----- From: "Misunas, Marla" Sent: Nov 17, 2003 1:06 PM To: mcn-l@mcn.edu Subject: Archival fixed storage media Hi everyone, At SFMOMA we are beginning to archive some large raw image files (our servers are getting full) and are looking to tap into your information/experience on the elusive question of which fixed storage media we should use -- now.  Should we use Kodak’s Gold Ultima?  Should we use DVD?  Does anyone have information on predicted longevity for DVD?  Is there a specific type of DVD we should use?  Is there an archival alternative to DVD?  Which different redundant media storage formats are recommended?  Does anyone (really) migrate their fixed media every few years?  Any issues about migration we should look out for? We’ve tossed these questions around for quite a while and we are familiar with many resources (such as the Colorado Digitization Program) but as our field is always updating itself, I wanted to check in on any current thinking/research, etc.   --- You are currently subscribed to mcn_mcn-l as: rlancefi...@mail.wesleyan.edu To unsubscribe send a blank email to leave-mcn_mcn-l-12800...@listserver.americaneagle.com --- You are currently subscribed to mcn_mcn-l as: y...@ucalgary.ca To unsubscribe send a blank email to leave-mcn_mcn-l-12800...@listserver.americaneagle.com