ODA_White_Paper_v110

Optical Disc Archive
White Paper



                          Version ‐ 1.10

Sony Corporation, Professional Solution Group,
Content Creation Solution Business Division
December 2012

Optical Disc Archive White Paper 2

1. Background
While the general trend in the professional audio/video media industry has moved
steadily from its tape based origins toward file based workflows for acquisition post
production and distribution, the archive domain has remained largely tape‐based.  Now is
the time to consider this final and all important final stage of the production process.
As a leading broadcast equipment manufacturer Sony is very consciously aware of the
challenges facing many broadcasters with regard to their media archives. While there
remains uncountable hundreds of thousands of hours stored on the long legacy of Sony
video tape formats including  Betacam, Betacam‐SP, Digital Betacam, D1, D2, HDCAM and
most recently HDCAM‐SR, the message from our customers remains loud and clear – they
want an alternative to tape for long‐term archive storage! Likewise in the case of the film
industry, archivists have been reluctant to transfer film to tape, even the most modern
digital data‐tape formats are considered by many to offer insufficient benefit, in terms of
archival life, to the original film stock.
The most common complaint from the user community is the constant need to migrate
valuable assets from one form of tape or hard‐disk media to the next simply to maintain a
viable archive. This requirement for Copy Migration, coupled with the well‐known and
understood issues associated with long‐term storage of film and tape media in respect of
environmental conditions, susceptibility to damage by flooding and other natural disasters
continue to challenge the continued use of the traditional carriers. Furthermore, the true
cost of ownership of maintaining these large media archives on media which demands
constant environmental controls and power hungry data centres is becoming more and
more unacceptable in an increasingly environmentally friendly world.
It is against this background that Sony turned its attention to the problems facing
archivists world‐wide. We have listened carefully to our customers in the broadcast media,
sound and film archive communities in every part of the world where we operate and have
challenged our research and development groups to seek a better alternative.
Not surprisingly, our attention turned towards optical recording techniques and optical
disc in particular. While the capacity per media and data transfer rates associated with even
the latest Blu‐Ray discs do not compare favourably with modern data‐tape, the fact remains
that optical discs are considerably more durable than hard‐disk storage systems or magnetic
tape based media.
The choice of technology for large media archives is clearly not one to be taken lightly,
and once committed the requirement to perform copy migration every several years is no
longer acceptable. The historical track‐record for optical disc technology in terms of
generational compatibility is very encouraging. Even the earliest music CDs and CD‐ROMs
introduced the early 1980’s remain compatible with the latest Blu‐Ray players (Fig.1‐1) ‐


driven largely by the very significant mass market for optical disc storage media. This is a key
consideration, and it can be expected that this trend will continue in the future.

                                                                          Figure 1‐1

2. “Optical Disc Archive” – New Storage System
It is against this background which Sony has sought to address the key shortcomings of
optical disc as an archive carrier – namely capacity per media, and data transfer rate. The
result is an all new optical disc based storage system, based on Blu‐Ray technology, but
inheriting some key attributes from Sony’s Professional Disc (XDCAM) which has enjoyed
very widespread success by the broadcast and professional video production community
since its introduction in 2004.
The proposed new “Optical Disc Archive” Storage System involves the use of multiple bare
discs contained within a very robust cartridge and a dedicated disc drive unit with an
associated software driver able to manipulate the discs individually – providing a seamless
read/write capability.

                 Photo 2‐1. “Optical Disc Archive” Drive unit & Cartridge


The highly compact disc cartridge is designed to hold 12 optical discs and is sufficiently
robust to withstand the rigours of any typical robotic storage system – and much more. In
addition to all of the standard acceleration tests for removable media it has been tested in a
variety of extreme handling conditions.
The drive is contained within standard 5‐inch full‐height housing and as such may be easily
accommodated within a variety of robotic systems – if required.
This white paper seeks to outline the key characteristics and features of the recording
media the cartridge and drive mechanism as well as the associated file system.

3. Optical Disc Archive ‐ Recording Media
3.1 Media Product Range
The “Optical Disc Archive” cartridge may be populated with a variety of compatible disc
media, including options for both Write Once and Rewritable discs – according to the needs
of individual users and their particular applications, as shown in Table 3‐1.

Table 3‐1


3.2 Basic Recording Mechanism
“Optical Disc Archive” media is based on phase‐change recording technology. Optical
objective lenses concentrate laser light onto microscopic beam spots. By scanning these
spots along a spiral track on the recording surface of the disc, the system is able to record
and recover the data.
The size of each spot is determined by the numerical aperture (NA), which corresponds to
the power of the objective lens, and by the wavelength () of the laser. As NA increases and
the wavelength () shortens, and the spot becomes smaller. The result is high spatial
resolution and high density. The “Optical Disc Archive” uses a blue‐violet laser providing a
wavelength of 405nm. This is very considerably shorter than the infrared lasers used for CDs
(780nm) and the red lasers used for DVDs (=650nm). The NA of the objective lenses is also
increased, while the thickness of the substrate, through which the recording laser beam
passes, is reduced (Figure 3‐1).
Figure 3‐1. Comparison of Recording Densities, Optical Parameters
and Structures of Optical Discs

The optical aberration caused by a tilting of the disc substrate increases in proportion to
the cube of the NA and the thickness of the substrate. To avoid reducing the tolerance
associated with tilting the disc, it is necessary to make the substrate thinner. A CD has a
1.2mm substrate, while a DVD consists of 0.6mm substrates bonded together. The recording
surface of the “Optical Disc Archive” is coated with a 0.1mm transparent protective layer
through which it is exposed to the laser beam.
The recording materials in phase‐change optical discs are made from alloys with relatively
low melting points (approximately 600ºC). Key ingredients in these materials include
Germanium, Antimony and Tellurium. When they are heated above their melting point and
then rapidly cooled after melting, these substances have the property of solidifying in an


amorphous state (without crystallization, and with the individual elements positioned
randomly). When amorphous solids are heated above a certain temperature (the
crystallization temperature), they rapidly begin to crystallize. With an optical disc, it is
necessary to heat the material and complete crystallization within the extremely short time
required for a highly‐focused laser beam to pass through, in practice, approximately 10
nanoseconds.
By controlling the power of this laser exposure, it is possible to record, erase and rewrite
data through repeated and reversible transitions between the amorphous and crystalline
states. The principle used in the recovery of data is that the differences in reflectivity
between those two states cause variations of reflected light intensity, which can be detected
via an optical pickup system. As in the case of other phase‐change discs, the “Optical Disc
Archive” has an optical design in which the reflectivity is lower when the material is in an
amorphous state, indicating the presence of a recording mark.

                       Figure 3‐2.  Phase‐change Recording Principle and Playback Signals
   Figure 3‐2 shows the relationship between the playback signals detected in reflected light,
the laser power waveform and the resulting crystalline structure in the recording film. To
form recording marks, the recording film is exposed to high‐power laser light with the laser
operating in short‐pulse mode. The recording material at the exposed location is
instantaneously heated above its melting point and then rapidly cooled, leaving it in the
amorphous state. When an erasing power pulse at the level needed to raise the temperature
above the crystallization point is superimposed on this writing pulse, previously recorded
marks in the amorphous state are first deleted, allowing data to be overwritten directly in a
single laser beam scan.
By modulating the laser power, the system can create marks and spaces on the recording
surface ranging in length from 2T to 8T where “T” is a length equal to 1 clock period. While


the disc is rotating on the spindle, the drive system’s servomechanism, both tracking and
focus servos, control the position of the laser such that it is directly over the appropriate disc
track at a specified distance. The laser is then pulsed while the reflected laser beam is
measured to verify and control the laser power.
When writing these marks, the laser power is actually pulsed in short increments to
ensure that the marks generated are clean, symmetric, and thus easily read. If the laser
power is not pulsed, marks have a tendency to form in a “teardrop” shape, making it more
difficult to read accurately.  Figure 3‐3 shows a graphic representation of the specific manner
in which data is written.
2T
Mark
2T
Space
5T
Mark
3T
Mark
4T
Mark
5T
Space
8T
Space
Writing
Power
Erasing
Power
Cooling
Power
Disc
Recording
Track
NRZI
Converted
Signal

Figure 3‐3.  Actual Writing Laser Pulse Form

Figure 3‐4 compares the grooves formed on the disc substrate by direct observation via an
atomic force microscope (AFM). The groove forms a spiral track running from the inner edge
of the disc to its outer circumference. This is used as a tracking guide for the laser beam. It
can also be used to provide access control signals by modulating address information by
means of minute wobbles with amplitude of just over 10nm.

Figure 3‐4.  Recording Layer Track Pitch and Wobbled Grooves
                                                 Compared to DVD+RW Format


A similar address signal system is used in the DVD+RW format. In the case of the “Optical
Disc Archive”, however, the track pitch and wobbling amplitude must both be created on the
master disc (Note 1) with far greater precision.
(Note 1): A master disc is a metallic disc used to replicate high‐precision grooves onto plastic substrates. It is
produced using semiconductor lithography technology.

3.3 Reliability
Typical reliability test results against accelerated environmental conditions are outlined
below.
Figure 3‐5 shows short term storage tests under severe environmental conditions. The
upper pair of graphs shows results for “Optical Disc Archive” media stored for 2 weeks at
minus 40 degrees Celsius. Evaluation of the symbol error rate (equal to Byte error rate in this
case) between before and after the experiment shows no significant error rate change and
no damage to the discs. The lower pair of graphs shows the result of the heat cycle test,
where discs are exposed at ‐40 degrees Celsius for 6 hours to up to +60 degrees Celsius for 8
hours, repeated for 4 cycles.  This heat shock experiment also shows no significant error rate
change and no damage to the discs.

Figure 3‐5.  Heat Shock Test

Figure 3‐6 shows the test results when the media is subjected to a highly corrosive gas
environment. Mixtures of hydrogen sulfide (concentration; 0.07ppm), nitrogen dioxide


(1.4ppm), chlorine gas (0.07ppm) and sulfur dioxide (1.4ppm) corrosive gases were
introduced into the environmental test chamber. The temperature and relative humidity
were kept at 35 degrees Celsius and 85% humidity during the storage experiment for 295
hours.

Figure 3‐6. Storage Test under Corrosive Gas Environment
This aging test is based on the corrosive environmental test conditions specified by the IEC
(International Electro‐technical Commission) Method‐4 (revised). Almost all devices which
pass this form of accelerated test are considered to be safe from corrosion for over 30 years
under normal environmental conditions. No corrosion or error rate change in the “Optical
Disc Archive” was detected following this aging test.

The estimated longevity for “Optical Disc Archive” media using the accelerated
temperature and humidity aging test is presented in Figure 3‐7. Discs were stored in
environmental test chambers in which the temperature was kept at 60, 70 and 80 degrees
Celsius (at 85% relative humidity). Degradation in error rate versus storage time was
measured for each aging condition. We estimated average media life end to be at the point
at which the error rate increases to the criteria of error correction for each temperature.
Figure 3‐7 shows the result of well‐known “Arrhenius plot” (same as ISO/TC42/SC N4296
Acceleration Test Method for Magneto‐Optical Disc Media), where the horizontal axis is a
reciprocal of the absolute temperature for aging and the vertical line is the end of life time
for each condition. Extrapolation to room temperature indicates that the average media life
is over 50 years.


Figure 3‐7. Long Term Storage Test under Accelerated Temperature
Further stress testing has been conducted using ultraviolet irradiation. This method was
originally standardized for the purpose of testing fading characteristics of dyed textiles but is
now also used for light exposure testing of DVD‐R media. Based on the international test
standard ISO 105‐B02:1994, ultraviolet light of 1w/m2 exposure power by a Xenon arc lamp
is irradiated onto the recording surface of the disc for 15 hours at 45℃ and 70% relative
humidity. The error rate is stable and remains unchanged after the test as shown in Figure 3‐
8.

Figure 3‐8. Xenon arc fading lamp test
In the case of the “Optical Disc Archive” 12 discs are housed in robust and air‐tight
cartridge, which prevents contamination or damage to the surface of the discs. Furthermore,
the recording surface is further protected by a very special transparent 0.1mm hard coating.
The thin coating itself has some excellent properties of its own, which assure stable and
reliable read/write performance.


The scratch protection properties of the coating are shown in Figure 3‐9. The photos on the
left show the results of the “Taber” abrasion test. The surface of a conventional DVD shows
obvious damage after typically 5 applications of the abrasive “Taber” abrasion tool. By
contrast however, there are almost no signs of abrasion on SONY’s “Optical Disc Archive” as
each disc is coated with highly scratch‐resistant hard coat. Figure 3‐10 shows the durability
of the protective hard coating against abrasion. The specification of abrasion properties of
consumer “Blu‐ray writable bare disc” is that the error rate should be lower than that
indicated in the figure after five rotations of abrasion tool. However, the hard coat layer
applied to the “Optical Disc Archive” media remains intact even after hundreds of rotations.

Figure 3‐9. “Taber” abrasion test

Figure 3‐10. Durability of SONY Hard Coat Cover Layer against abrasion


The surface coating also has important stain resistant properties; it helps to keep the
surface of the disc clean and is particularly effective for reducing the interference of by
accidental handling including contamination by finger‐prints. The microscopically magnified
photos in Figure 3‐11 show a line on the surface of a disc made with an oil‐based felt‐tip pen.
The outline of oil‐based ink is clear and solid on a non treated surface. However, the coating
applied to the “Optical Disc Archive” media effectively repels the ink – as shown on the
photo on the right.

Figure 3‐11. Stain resistant property of the hard coating
A fingerprint stamp test is shown in Figure 3‐12. With no stain protection, oily residues are
present on the image shown on the left and significant interference, caused by the
fingerprint is observed in servo and RF signals. By contrast, the surface of specially coated or
“Optical Disc Archive” media effectively repels the oily residue. Consequently, the
disturbance seen in the servo and RF signals in read/write process is significantly reduced ‐
as indicated on the right.

Figure 3‐12.  Anti‐Fingerprints Property of SONY Optical Disc Archive


The anti‐static properties of the coating are shown in Figure 3‐13 and Figure 3‐14. Figure 3‐
13, shows attenuation curves against electrostatic charge after static electricity is forcibly
applied to the discs. With no anti‐static coating, as in the case of conventional CD and DVD
discs, the applied electrostatic charge is hardly reduced even after 120 minutes. However
SONY’s “Optical Disc Archive” media with high performance hard coating easily discharges
the static electricity and the electrostatic charge is quickly reduced to less than half the
initial level after only 120 seconds. Consequently, SONY’s “Optical Disc Archive” media
effectively minimize the accumulation of dust in the operating environment.

Figure 3‐13. Attenuation Curve of Electrostatic Charge

The photos in Figure 3‐14 show an example of dust adhesion on discs caused by a frictional
electrification. In this experiment, the surface of the disc is wiped with a tissue paper several
times and thus given a charge. Then, office dust is brought into close proximity to the disc.
As we see in these photos, the conventional disc attracts a considerable amount of dust.
However, almost no dust adheres on the SONY’s “Optical Disc Archive” media. The presence
of dust particles naturally affects data read/write performance. While there is some
degradation of the Symbol Error Rate (SER) in the area of dust adhesion for conventional disc,
whereas practically no SER variation is observed over the entire surface of the SONY “Optical
Disc Archive” media.


                              Figure 3‐14.  Dust Adhesion Test by Frictional Electrification
In conclusion, the high performance coating developed for the “Optical Disc Archive”
provides far more than just scratch‐resistance, but also stain resistant especially against
fingerprints and anti‐static characteristics. These properties of the coating considerably
reduce accidental risk of scratching and/or contamination, despite the additional substantial
protection provided by the cartridge in normal use.
   In addition to normal environmental conditions, storage media used to preserve valuable
archival data ought to be able to survive natural disaster, particularly flooding. The sea water
soak test is outlined in Picture 3‐1. Recorded “Optical Disc Archive” cartridges were
submerged in seawater for 5 weeks. The cartridges were then recovered and rinsed with tap
water before being dried at room temperature. While slight rusting was observed in some
areas of the clamping plate there was no corrosion or damage of any kind to the discs
themselves. All the recorded data was recovered with no failures.

Picture 3‐1. Soak test of the “Optical Disc Archive” cartridge in seawater


Note) All the experimental data shown in the chapter 3.3 is the result of single layer
rewritable disc. The actual result may be different depending on the conditions.
3.4 Cartridge Design
The new “Optical Disc Archive” system incorporates a robust and compact cartridge, which
holds 12 bare discs. The key physical parameters of the cartridge are illustrated in Figure3‐15.
The shape of the cartridge is almost square (130mm in length, 132mm in width, and 26.7mm
in height). The weight of the cartridge is approximately 320g including 12 discs. This compact
cartridge is made from polycarbonate resin, well‐known for its heat‐proof qualities; it
provides a durable and dust‐resistant shell for its precious contents.

Figure 3‐15. “Optical Disc Archive” Cartridge Design
All the main components, including the internal mechanical parts and of the cartridge are
shown in Figure 3‐16 and Figure 3‐17 respectively. Once loaded in the “Optical Disc Archive”
drive system, the upper shell of the cartridge (including front & back shells and several small
parts) is physically separated from the lower shell, which contains the 12 discs, by releasing a
pair of locks. The sideboards at both ends of the lower shell have twelve “grooves” on the
inside surface which support the disc pack ‐ as shown in Figure 3‐16. The lower shell
assembly is reinforced via a simple “metal bridge” between the two sideboards. Once the
cartridge is ejected from the drive system, the upper and the lower shells are re‐united and
then locked tightly together, to hold the discs securely. The “center pillar” of the upper shell
forms a structural pillar between the lower and the upper shells. This provides very
considerable mechanical strength to the structure and serves to protect discs and their
precious contents from load pressure, shock and vibration.
Cartridge Size : 130mm(W)×132mm(D)×26.7mm(H)
Weight : approx. 320g (including 12 discs)
Label Area
(Top View) (Bottom View)
Write Protector
Gripper Slot



        Figure 3‐16.  Inside Mechanism of the Cartridge
This compact but high capacity optical multi‐disc cartridge is also intended to be handled by
robotic systems in mass‐storage libraries. With this in mind the cartridge has been carefully
designed with this purpose in mind and incorporates two pairs of slots, located on the lower
shell to facilitate secure handling by mechanical grippers.
Each “Optical Disc Archive” cartridge contains a built‐in RFID tag (Radio Frequency
IDentification) as shown in Figure 3‐17. The RFID tag uniquely identifies each individual disc
so that the content can be easily identified using a variety of compatible RFID readers and
mobile devices for effective asset management.

                                      Figure 3‐17.  Main Components of the Cartridge
Upper Shell
Write Protector
Back Shell
Front Lock(R)
Lower Shell
Spring
Front Lock(L)
Front Shell
Back Lock(R)
Back Lock(L) RFID
Metal Bridge
FS Plate


Thus far, this whitepaper has sought to explain the main features and functionalities of the
components used in an “Optical Disc Archive” cartridge, specifically designed for a long‐term
archiving purpose. We strongly believe that the new “Optical Disc Archive” represents a new
frontier for media asset management, made possible by Sony’s long history of Professional
Media development and production capability.  What follows is a description of the drive
unit and the associated file system.

4. Optical Disc Archive ‐ Drive Unit
The dedicated drive unit is built in two parts comprising the read/write platform and its
integrated multi‐disc handling mechanism. The complete drive is contained within standard
5‐inch full‐height housing and as such may be easily accommodated within a variety of
robotic systems – if required.
The read/write mechanism is based largely on the latest XDCAM drive technology, and as
such benefits from the proven reliability and track record of the past 8 years or more. The
basic read/write platform is able to accommodate all available multi‐layer discs, including re‐
writable and write‐once media.
The “Dual Channel Head System” incorporates two optical read/write heads mounted on a
single head assembly (Photo 4‐1). This dual channel head assembly delivers twice the data
rate of a single optical head.  Using this design, it remains technically feasible implement a 4
head read/write system, thereby further doubling the data throughput.

                                                   Photo 4‐1.
The ODS‐D55U is the first “Optical Disc Archive” compatible drive. The front and rear view
is shown in the photo 4‐2. It supports a USB 3.0 interface and as such can be simply mounted
as an external drive, via the supplied software driver.


                                                                   Photo 4‐2.
The ODS‐D55U drive unit supports an additional recording mode called “write‐verify” mode.
In this mode, while the file is being written to the disc, the recorded data is simultaneously
read to confirm the recording process. In this mode, one laser head acts as the “write” head
while the second laser head acts as the “read” head and as such the overall data transfer
rate is reduced by approximately half.
Optical disc recording is by nature extremely reliable, thanks largely to the non‐contact
nature of the recording mechanism. Indeed, in the case of the XDCAM Professional Disc no
such write‐verify mode is provided and real‐world experience over the past eight years or
more has been excellent.  That said, the “write verify” mode is provided in the case if the
“Optical Disc Archive” as an option, in recognition of the very nature of data archive and
back‐up applications and the current trend among users to verify the data integrity after
each read/write process.  The “write verify” mode is a user selectable option provided in the
supplied Software Utility.

The random access nature of the medium provides for faster access times than can be
achieved with tape, and in typical use cases involving multiple file retrieve and indeed partial
file retrieves, practical tests have shown that the faster speed of access more than
compensates for the somewhat slower data transfer rate. However, actual data‐rates are
sufficient to allow for real‐time video replay, direct from the archive media – a highly
desirable feature for search and browse operation.
Despite these advances and the use of multiple read/write heads and the resultant increase
in data throughput, the fact remains that “Optical Disc Archive” disc may be recovered by
means of a single optical laser reader, regardless of source of manufacture, thereby enabling
a very high degree to future compatibility – in much the same way that the latest Blu‐Ray
player is able to read an early Compact Disc or DVD disc.
Table 4‐1 shows the basic specification of ODS‐D55U.


Table 4‐1. Basic specification of ODS‐D55U

5. File system & File Format
5.1 File System
Users prefer a standard file system, with support for Drag and Drop User Interface via a
selection of operating systems.
Figure 5‐1 shows the file system hierarchy for the “Optical Disc Archive” in comparison with
the standard Blu‐ray disc format. The file system for the “Optical Disc Archive” is fully
compliant with the industry standard UDF (Universal Disk Format) and ECMA. However, due
to the fact that the “Optical Disc Archive” format must accommodate multiple discs within
the cartridge, some additional rules and restrictions on the use of UDF apply. However, there
are no definitions for Audio/Video recording as in the case of Blue‐ray disc (Part 3) as the
format is able to accommodate all data file types.

Figure 5‐1. Format hierarchy


In normal operation, the cartridge is mounted as a single media, and the driver software,
which is open to industry partners, manages the transition between individual discs ‐ to
provide seamless storage over multiple discs. The “Optical Disc Archive” supports the
concept of “Volume set” as defined in ECMA‐167/UDF and shown in Figure 5‐2. “Volume set”
implies a collection of one or multi volumes. In this case “volume” means one physical “disc”,
and the “Optical Disc Archive” uses multi volume set, while Blu‐ray uses a single volume set.

Figure 5‐2. Volume set
It is by using this Multi Volume Set that the “Optical Disc Archive” format is able to be
mounted as one large logical volume through the file system driver.

5.2 Third Party Support
While the necessary Software Drivers are supplied with each Drive Unit, Sony recognises the
important role played by an increasing number of third party manufacturers involved in the
realisation of system solutions for media archive applications. As such, Sony has established
alliances with several key industry leaders, all with a view to secure the longevity of the
system through multi‐sourcing of key components, including the media itself. The program
will be targeted to those manufacturers involved in related business areas such as storage
media, robotics (automated media exchange systems) middleware (hierarchical storage
management & control) and application software for media asset management (including
media management and search).
5.3 Sequential Recording & File Spanning
In the case of the “Optical Disc Archive” format, data is recorded sequentially on the disc
for both write‐once and re‐writable – as outlined in Figure 5‐3 below.


                                                  Figure 5‐3. Sequential recording

1. When a new cartridge is loaded into the drive, it is logically formatted and the first file
system is recorded.
2. After “file‐1” has been recorded, a new file system which describes the “file‐1”
information is created and recorded at the end of “file‐1” record.
3. Subsequently, when “file‐2” and “file‐3” are recorded, a new file system which describes
files 1, 2 and 3 information is created and recorded at the end of the “file‐3” record.
4. If “file‐1” is subsequently deleted, the file system data is updated and recorded. The
deleted file data still physically remains on the disc, but is not referred in the updated file
system record. Note: Available capacity is not increased, but rollback function is
supported.

As outlined above, the “Optical Disc Archive” file system accommodates large files which
might exceed the capacity of a single bare disc and as such a single file might span across
multiple discs. This “Spanning discs” process is performed by the file system driver
automatically and is outlined in Figure 5‐4 below. Note that the application layer software
need not be aware that the file is spanned or not.
When “file‐2” is recorded and the available capacity of “Disc‐1” is to be exceeded, the file
system information which describes the contents of “Disc‐1” is recorded at the end of “Disc‐
1”, and the subsequent data is recorded on “Disc‐2” and the process is repeated from “Disc‐
N” to “Disc‐N+1”.


Figure 5‐4. File spanning
When the cartridge is ejected from the drive, the disc number where the latest file system
is recorded is stored to the cartridge memory and when the cartridge is loaded this disc
number in the cartridge memory is read first and the disc which includes the latest file
system is immediately loaded. For this reason, the Mount Time when the cartridge is loaded
is relatively short compared to the XDCAM system even though “Optical Disc Archive” drive
handles 12 discs at a time. The latest file system shows the entire folders/files/metadata
information in the cartridge through the browser. If the file on the current disc is selected its
access is immediate and if the file on a different disc is selected the file system driver
automatically change the disc to access to the target file. The disc change process time is
constant regardless the location of the target disc in the cartridge.

5.4 Rollback Utility
When the “Optical Disc Archive” file system driver is installed, the Software Utility is also
automatically installed. This Graphical User Interface (GUI) provides a variety of useful utility
functions. Basic drive information (hours meter, firmware version, cartridge loading number,
error log etc.) are shown and some other functions such as Format & Finalize can be
performed.
Furthermore, the “Optical Disc Archive” format also supports a “Rollback” function through
the same GUI. Rollback enables the File System to be rolled back to any arbitrary point in the
past. This feature is based on the fact that as a sequential recording medium, the file data
and the file system data not physically erased.


                                                                        Figure 5‐5
Consider the case when, after a new cartridge is loaded into the drive and “file‐1” & “file‐2”
are recoded, then “file‐3” is added and “file‐2” is deleted. The respective file system
information is recorded as shown in figure 5‐5 above. In this scenario, the user would be
able to select one of two “Rollback Points”, depending on the media type.
Figure 5‐6 shows “Rollback without Restore” which is available for both write‐once and re‐
writable media. The same file system information is copied at the end of the record, which
reflects most recent (current) file system. In this case, no free disc space is recovered, but all
the entire file system remains intact and the possibility for further “Rollback” is retained.

                                             Figure 5‐6. Rollback without Restore
Figure 5‐7 shows “Rollback with Restore” which is available only in the case of re‐writable
media. In this case, all the data which was recorded after the “Rollback Point” is physically
deleted and free disc space is recovered, however it will not be possible to recover the file
system to a stage created after this point.

                                                 Figure 5‐7. Rollback with Restore


5.5 Cartridge Memory
As outlined in the chapter 3‐4., each “Optical Disc Archive” cartridge contains a built‐in
RFID tag (Radio Frequency IDentification). This “cartridge memory” is used in a variety of
ways.
The total capacity of cartridge memory is 8Kbytes, of which approximately 3Kbytes is used
for media and system information (e.g. unique‐ID, media type, life management information
etc.). The remaining capacity (about 5Kbytes) is available for use by the application software.
For example, if selected metadata (such as file name, or cartridge description etc.) is copied
from the disc to the cartridge memory by application software, then that information can be
read by a suitably equipped smartphone or other device. This feature enables important
cartridge information to be read without the need to load the cartridge into a drive unit.

5.6 Additional Parity
In order to provide even more robustness for archival use, an additional “parity mechanism”
in addition to the Blu‐ray error correction is implemented in the file system driver. Less than
1% parity data is added to the actual data and recorded. The parity data is computed and
written by the file system driver automatically during the write operation. However the
added parity data is not accessed by the file system driver during the normal read process.
Damaged files may be recovered using the parity data via the “file recovery” function
provided by the Software Utility.


6. Conclusions
The “Optical Disc Archive” ensures archival life of more than 50 years and eliminates the
need for on‐going Copy Migration. The very nature of the media and the recording process
means that the environmental conditions for media storage may be considerably relaxed by
comparison with that for tape based media. Both of these factors contribute towards
significant savings in the total cost of ownership. Furthermore, the robustness of the media
in the event of natural disaster is a further significant advantage in the event of such
occurrences.
As a form of removable media the “Optical Disc Archive” may be deployed as a means for
the exchange of content between facilities and for storage of larger Non‐Linear Editing (NLE)
project files. For these and other such use cases, including off‐line Disaster Recovery
solutions, a managed shelf archive remains a very practical solution – for which the “Optical
Disc Archive” is also well suited.
The technology lends itself well to both off‐line (shelf based) and automated (robotic)
handling systems and the performance compares favourably with state of the art video tape
recorders, including the ability to support real‐time replay for search and browse.
It is expected that the system will be both well recognised and supported within the media
archive community via a targeted Industry Alliance Program, both in terms of
interoperability and multi‐sourcing of key components, including the media itself.


References:
Digital Dilemma – Strategic Issues In Archiving and Accessing Digital Motion Picture
Materials. The Academy of Motion Picture Arts and Sciences.
Accelerated Aging Test  ‐  ISO/IEC 10995:2008(E)
Universal Disk Format (UDF) ‐  Universal Disk Format® and UDF® are registered marks of the
OSTA(Optical Storage Technology Association). The OSTA Universal Disk Format (UDF®)
specification defines a subset of the standard ECMA 167 3rd edition. The primary goal of the
OSTA UDF is to maximize data interchange and minimize the cost and complexity of
implementing ECMA 167.

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