Over the last few months I have written a lot about magnetic tape, data recovery from magnetic tape, and the appropriate care and handling of these tapes and cartridges. SpectrumData is currently creating and writing data to more CDs and DVDs than ever before so I thought it may be time to pay a little more attention to CD & DVD media this month.
In recent editions of IT, PC and data storage publications, as well as online publications and forums, there have been a lot of articles and discussion regarding the life expectancy of optical media and whether the data stored on CDs and DVDs will be able to be reliably restored from archive when required in the future. In these articles there always seems to be some good news and some bad news. Which do you want first?
The Good News
The positive side of the debate is that manufacturers of optical media themselves are now openly talking about potential issues with the reliability and life expectancy of certain types of DVDs and CDs, particularly in relation to the usage patterns and storage conditions of the disks. The good news is that many manufacturers are now starting to address these issues with the release of improved technology and innovative media types which include new dyes and metal layers such gold.
The Bad News
The downside of this debate is that if you use a lot of writable and rewritable media (CD-R and RW, or DVD-R and RW) these new developments in optical media technology (the good news) may be a little too late for your vast music or family photograph collection or for your irreplaceable and valuable data.
Simply put, there are really three categories of disk available – ROM, R and RW.
ROM – Read Only Media
There is general consensus that pressed original CDs have a much longer life span than writable (R) or re-writable (RW) media. The main reason for this is the difference in construction of the media types. Pressed originals (ROMs) are generally made of an aluminium moulded data layer. The pressed aluminium data layer life span will be maximised if one can ensure that the aluminium data layer is not subjected to moisture. The best example of ROM media is the music CD you buy from your local music store or the CD containing software you received from when you bought your latest PC or laptop.
In humid areas and over time, the disks can absorb moisture which eventually makes its way to the aluminium layer which can cause its reflectivity to be reduced due to oxidation i.e. the lower the reflectivity, the poorer the read from the media.
R – Write Once Media
Write Once Media generally use dyes or film to record the data as opposed to the moulded metal of a ROM. These dyes and films are particularly susceptible to the extremes of light, temperature, and humidity variations found in the normal use of these media types. These dyes degrade naturally and variations in temperature and humidity as well as light conditions can expedite this degradation.
RW – Rewritable Media
These disks use a phase changing film with an aluminium reflective layer behind them. The film used in these disks is generally considered less stable than that of R media and by its nature needs to be that way to allow multiple writes to the layer. The layer is affected more by heat than by light but too much of either can accelerate the degradation process.
The Technological Advancements
Some of the improvements made by manufacturers in the optical media market that have made for a far superior ‘R’ and ‘RW’ product include:
- The use of gold as the reflective layer reducing the possibility of oxidisation of the metal backing layer.
- Enhanced high performance dyes for recording that are not as susceptible to degradation due to changes in light and temperature.
- Scratch resistant technology such as that found in the Imation Force field range.
- There has also been the release of ‘Blue Ray’ DVD which holds up to 50GB of data on a single disk. (NB - No one is complaining about the life span of this technology as yet as it is too new, but we will keep you posted)
What can you do to maximise the life span of your media?
- Buy quality media – you get what you pay for. SpectrumData recommend and only use Imation ForceField brand optical media
- Avoid extremes of light, temperature and humidity. Click here for SpectrumData’s Media Care & Handling Guidelines.
- Store the media in its case when not in use
- Only write once to the media if possible (if RW)
- Avoid bending the disks
- Only use approved labelling techniques
- And of course……... if you have a 3 year old child or a very excited puppy in the house… ensure that you keep the media out of reach!!
So, what is the life expectancy of optical media ?
How long will they last has as many answers as you like. If you read one article, it will say 2 years, while another still proclaims 100 years. After reviewing many articles on the subject I have come up with some average life spans for the different types of media. These are not fixed in concrete as all of the estimates depend on the brand of media, the dye used, the reflective layer materials, handling, storage conditions and a range of other factors. But rather than say that there really seems to be little or no agreement on the life span of optical, I though some general rules of thumb would be helpful.
- CD-ROM 30 to 100 years
- CD-R 5 to 10 years (depending on whether the CD-R was been written to or not)
- CD-RW 5 to 10 years (depending on how many times the media has been re-written to)
If you follow some of the simple rules to maximise the life span of your recordable media, you should get close to a decade of use out of them before needing to migrate your data to new media.
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