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Disc duplication can have one or more goals. There are three primary aspects to consider for disc duplication projects. Conclusions influence decisions related to disc media and recording techniques.
- Data Integrity
- Data Interchangeability
- Data Longevity
Data Integrity as related to disc duplication refers to the consistency and accuracy of data, files and directory structures being properly recorded to discs from the master. Ensuring that data integrity is correct on the master and resulting discs are recorded accurately and consistently, increases the probability that discs will be read and playback as expected.
It’s not about physical security or preservation of data. The old adage: “garbage-in, garbage-out” applies. Data integrity is about keeping garbage out and recording data file structures correctly using quality discs.
If the master contains garbage – in forms of defective, corrupted or incorrect content or data – then cloned discs will inherit the garbage. Before using any master disc for duplication, it’s imperative that the master be inspected and tested by its author or responsible person.
Confirming in advance that files can be opened, data is not corrupted and is readable, along with video files playing back properly from the master, will help avoid disappointments later.
If the master contains data, file and directory structures that are correct and readable, steps that ensure data integrity is recorded with duplicated discs can be determined by:
- The quality of recordable blank discs and their ability to accurately record content.
- Equipment quality. If duplication equipment is defective, obsolete, improperly maintained, constantly stressed through overuse, operated continuously at maximum levels or set-up incorrectly due to operator error – data integrity on duplicated discs can be compromised.
- Data integrity on discs can also be compromised by damage resulting from improper labeling, careless handling, defective disc packaging or damage during shipment and distribution of discs.
Data Interchangeability as related to disc duplication, refers to recorded discs being recognized, readable and playable across multiple manufacturers’ disc-readers and playback devices. Correct playback in various hardware is dependent upon both media and hardware manufacturers’ adherence to specifications for recording and playback of CD or DVD disc media.
Other factors can affect correct disc playback in hardware. These include:
- Duplicated disc media must reliably reflect laser light generated by PC readers and playback devices. Laser light that’s weak or faint may not be detected reliably by the pick-up sensor. When this occurs, read-errors force internal circuitry to attempt retries until read success is obtained or a time-out error occurs – stopping the disc. Continual attempts to read discs, reduces spin-rates and delays transfer of data. This can be particularly annoying with video content, because playback delays can cause motion glitches, image freezing or artifacts.
- Some disc readers or playback devices could have a weak, defective or misaligned laser. Firmware may have bugs. The disc media itself may be fine, but may not be readable by certain hardware. Testing disc playback in different readers can usually isolate and confirm either media or hardware related playback issues.
- If duplication equipment is of high-quality, defective or non-compliant discs are normally detected during recording – but not always. CD and DVD media specifications have long been finalized and most disc and hardware manufactures continually fine-tune their products to eliminate compatibility issues.
Data Longevity as related to disc duplication, pertains to the length of time data recorded to optical media remains useable. There are numerous factors that can affect the useable life of optical media – and the content they store. Archiving and preserving data can be very important.
- Over an extended period of time, the recording or 'dye-layer' within a recordable optical disc naturally degrades and experiences breakdown. As covered in the CD & DVD Physical Disc Structure section, of the OPTICAL TECHNICAL INOFRMATION page, the dye-layer records and stores digital bits that represent the actual content of a disc. Because recording dyes use organic formulations, they eventually deteriorate over long periods.
- As a disc’s dye-layer deteriorates, the individual “pits” that were optically altered by the recording laser to absorb light, begin to loose their opaque quality and become increasingly transparent – allowing laser light to pass through to the overlying reflective layer, instead of blocking light.
The contrast between darker pits and non-pitted transparent areas represent digital ones and zeros. Contrast reduction between areas can cause disc read-errors to occur. Over time, as sections of the dye-layer slowly deteriorate, disc read-errors increase. Eventually and subtlety, the disc will begin to loose larger amounts of data.
- CD and DVD readers have embedded firmware to detect and compensate for disc read-errors. However, excessive read-errors can represent a loss of data leading to disc failure.
- In the mid 1980’s when CD-R media was introduced, many discs experienced a phenomena referred to as 'data-rot'. Recorded disc data became unreadable in as little as two years. Eventually, improved production techniques employing better materials and chemical formulations improved overall disc longevity.
- Other factors that can impact disc life and data longevity include unstable dyes, corrosion on reflective layers, defective disc lamination and quality short-cuts during disc manufacturing.
- Not all disc media brands or types are equal. Some discs are better suited for preserving data than others. See: RECORDABLE DISC MEDIA IS NOT THE SAME
- Data longevity with optical discs can be determined by disc quality, recording methods, as well as disc usage, handling, environmental conditions and how disc are stored. See:
DISC HANDLING, ENVIRONMENTAL CONDITIONS, STORAGE & ARCHIVE
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