Blu-ray questions

Blu-ray Media and Storage Questions

Increasingly we are being asked the following questions from people we supply optical archiving solutions.

Data Format

Is the data format written on the disc an industry standard format? For example if you wish to archive information for 50 years, you want to use the most common and open supported standard. Currently this is UDF, Universal Disk Format which is the defacto standard for storing files on optical media. It is an implementation of the ISO/IEC 13346 standard (also known as ECMA-167). It is considered to be a replacement of ISO 9660, and today is widely used for (re)writable optical media. UDF is developed and maintained by the Optical Storage Technology Association (OSTA).

Industry Support

Is the technology supported by a large number of recognised industry names or is it a niche player?


Is the technology backed by organisations that have the financial strength and support to promote and provide the technology long term?

Media Costs

Will the cost of media likely to rise or fall? A primary example of this is DVD which when originally launched was £8 for a 4.7GB writeable disc. Now the cost of DVD 4.7GB discs has fallen to below £1.

Green Technology

With the escalating cost of electricity and the increasing threat of power outages, the philosophy of keeping everything spinning forever doesn’t make financial sense, especially if archiving for 5 – 50 years. Optical technology is ideally suited to archive infrequently accessed or static information. Most solutions which we provide have a disk cache on the front-end to improve searches and performance. Blu-ray as an archiving technology has a TuV certification of “B” which is lowest energy consumption of all data storage technologies.

Environmental Conditions

When archiving information long term, it is important to consider how the information needs to be stored.

  • Does it need to be stored at a certain temperature or humidty level?
  • Does the media need to be checked or retensioned?
  • Is it waterproof?
  • Is it dustproof?
  • Is it scratchproof?
  • Is it durable and robust?

Cartridge Media

UDO use a cartridge for media protection. BD discs were supposed to require a cartridge or a special coating to protect the disc, but later this idea was abandoned. Furthermore, TDK have to developed a hard coating called Durabis that complies with the Blu-ray specifications for the disc and is 100x more resistant to damage and fingerprints than a current DVD.

Backwards Compatibility

Can future generations of technology read the previous versions? A great example of this is Blu-ray which can read CD & DVD discs created 20 years ago!

Proliferation of Readers

With any archived storage technology we all know that the data written today can be read. Companies and organisations carry out periodic reviews of hardware and software. Eventually after 5-10 years that orginal hardware used to create all this archive information will end up in a skip. After 20 years that information might be needed for a legal case.

A classic example of this is the BBC, who in the early 80’s wanted to create an optical archive of doomsday information. After 15 years there no machines left to read the optical discs and a consortium of Universities had to make a machine capable of reading the discs.

Another example is that there are currently, at the time of writing, 10 million projected Blu-ray players being sold in 2008. It would be safe to assume that after 20 years some of these players will still exist.

Proprietary Technology

A single source of anything is not a wise business move. Should that company suffer financially, economically or suffer a takeover, what guarantee do you have that the archive technology you have sourced will still be widely available and if even those guarantees did exist, would it be financially viable to carry on using the technolgy?


All companies today offering archival storage, use accelerated testing results to prove the media used will be stable in 50, 100 or 200 years. Therefore we can only base any archive technology on this accelerated testing, otherwise nothing would be sold.

Recording Format

Both UDO and BD use a Blue laser for recording and both methods employ Phase-Change recording uses a layer of a special material (called the phase change layer) that can be changed repeatedly from an amorphous (formless) to a crystalline state, or phase-through exposure to variably-powered beams.

Error Rates

Blu-ray recorders have a Soft Read Error Less than 10-9 and a Hard Read Error Less than 10-12. Both UDO and Blu-ray employ a variant of Reed Solomon for error recovery.

Blu-ray uses a new error correction strategy, also based on Reed-Solomon codes, called LDC (Long Distance Code) and BIS (Burst Indication Subcode). The LDC parity bytes are RS (248,216,33) codes operating on data columns. The BIS blocks contain control and addressing information, which are protected by independent RS (62,30,33) codes. These BIS blocks are organised in 3 ‘picket columns”, evenly spaced between user data. The idea of these ‘pickets” is as follows, when errors are detected in two consecutive BIS codewords, it is likely that this was caused by a burst error, thus that lots of data bytes between these two columns are bad. This information can then be used as erasure indications to increase the correction capabilities of the LDC codes.  On top of this, two diagonal interleaving steps (similar to what is used on CDs) further decrease the impact of burst errors on error correction.

What Blu-ray Disc variants are available?

As with CD and DVD, Blu-ray Disc media comes in pre-recorded, recordable and rewritable variants. The pre-recorded disc is called BD-ROM, and usually contains movies or re-issued TV shows in High Definition format. The recordable disc is called BD-R, and can be used for archival of huge amounts of data or video. The rewritable disc is called BD-RE, and offers the same large capacity in a disc format that allows for repetitive usage.

What is the capacity of a Blu-ray Disc?

All three Blu-ray Disc types come in two versions: single layer and double layer. A double layer disc may hold up to twice the amount of data or video compared to a single layer disc, and uses two independent layers placed on one side of the disc to store its information. A single-layer disc holds up to 25 gigabytes, while a double-layer disc holds up to 50 gigabytes of data, without the need to flip the disc. The planned capacity for a Blu-ray disc is 200GB 8 layered disk of which TDK have successfully produced.

Can Blu-ray Disc products play DVD and CD?

Although this is not a requirement of the Blu-ray Disc format, it is very likely that all Blu-ray Disc products will play their DVD and CD counterpart formats. Compare this to the ability of today’s DVD players to play CDs. Most companies have developed laser components and pick-up units being able to read CD, DVD and BD.

Can Blu-ray Disc products record DVD and CD?

Implementation of DVD or CD recording capability is a manufacturer’s option. Currently, some Blu-ray Disc video products allow you to record DVDs as well. It is expected that most Blu-ray Disc PC drives will support the recording of CD, DVD and BD.

Can I play a Blu-ray disc on my DVD player?

No. As DVD players use a red laser to read the information from a disc, they are not capable of reading the very fine pits of a Blu-ray Disc, which requires a blue laser. Furthermore, DVD-Video players lack the advanced technology to decode the High Definition picture from a Blu-ray Disc.