圖出自上文中 NIST 的測試，400 小時大約十六天，800 小時超過一個月。放在這樣機車的環境中十幾天，不算太短吧?!




另外，


Care and Handling of CDs and DVDs: A Guide for Librarians and Archivists
(by Fred R. Byers, October 2003)
http://www.clir.org/pubs/reports/pub121/sec4.html

內文中提到建議不使用的原因：

(1) 相變材質衰退的速度較染料快。
(Rewritable discs use a phase-changing metal alloy film for recording data and aluminum for the reflective layer. The alloy film is not as stable as the dye used in R discs because the material normally degrades at a faster rate)

(2) 每覆寫一次保存的壽命減低，只寫一次的話應可撐稍較久點。
(This rewriting does, however, affect disc life expectancy; RW or RAM discs archived after the first recording should have a longer life expectancy than those that have undergone several erase-recording cycles.)

(3) 怕資料被不小心抹掉 (個人認為這個發生機率很低)。
(Information on RW and RAM discs is susceptible to loss or alteration as a result of the rewriting. Information on R discs is more secure precisely because it cannot be changed or rewritten.)



在「Using CDs for Data Storage」這篇文章中，也有提到 degrade 較快的問題，他是這樣寫的：「But even though this process guarantees that there is no way to retrieve erased files, the film layer used in these discs degrades at a faster rate than the dye used in CD-R discs, especially with frequent recording and re-writing. Thus, CD-RW discs should only be used for transferring files or for short-term use. They should not be used for data storage.」

因此，只寫一次也好，寫很多次也好，通通都有這個問題。只是多次寫後更糟而已。 不用去假設 Degrade 只有發生在重複寫入。


另外，在「VIDEO MEDIA GUIDES -> Blank Media & Quality FAQ」中關於「Optical phase change media」這部分，亦有類似敘述：

Unlike dye-based or pressed media, phase-change crystalline surfaces can degrade rapidly, whether the disc has been used or not. In time, these particles begin to break down, sometimes in as little as 6 months. The most common tell-tale sign is small craters form in the disc surface, causing unreadable areas. These craters can range from the size of a penny to the size of a pinhead, so they can be difficult to see with the naked eye. But because data is written into tiny grooves, especially DVD data, the smaller crater can cause catastrophic loss of information.

Phase change media was created for temporary re-usable situations. It is not archival and should never be used for something that needs to be kept longer than a few weeks. Some empirical data suggests that DVD-RW lasts longer than DVD+RW, and that DVD-RAM is not as affected by this (although not entirely immune). The simple solution is to not use phase change media except when absolutely needed for temporary storage.