Terabyte and Gigabits/s Archival Storage
Using Flexible Optical Disks
Haruki Tokumaru, Daiichi Koide, Takeshi Kajiyama, Yoshimichi Takano,Nobuaki Onagi*, and Koji Tsukahara*
Science and Technology Research Laboratories, Japan Broadcasting Corp. (NHK)
1-10-11 Kinuta, Setagaya, Tokyo 157-8510, Japan
Phone: +81-3-5494-3229; E-mail: tokumaru.h-dy@nhk.or.jp*Research and Development Group, Ricoh Company, Ltd.
16-1 Shinei-cho, Tsuzuki, Yokohama 224-0035, Japan

1. Introduction
Nonlinear storage such as hard disk drives, optical disk drives, and semiconductor memory arespreading in place of video-tape recorders (VTRs)—which have been used for program production by
TV stations for over 50 years. In the meanwhile, VTR tape is still the main and unique storage medium
for archival application, namely, preserving programs for a long time. For example, a huge amount of
VTR tapes (i.e., more than 700,000) have piled up at NHK over the years (Fig. 1). However, new kindsof preservation media are expected to replace VTR tapes for archival application because several typesof VTRs are going out of production and nonlinear-storage technologies are being demanded forarchival application.
Optical disks have a lifetime more than 50 years. Moreover, as the CD players have already proved,
reading devices will be supplied over a long time owing to the long product life of an optical disk. In
addition to these merits regarding archival application, optical disks are an inexpensive form of archival
media. However, compared to tape media such as linear-tape-open (LTO) systems which are widelyused as backup and archival application, optical storage is seriously lacking in terms of performance,
namely, capacity and recording speed.
A flexible optical disk (FOD) fabricated on a very thin (0.1 mm thick) polycarbonate substrate seems
to be a recording medium to break the performance barrier concerning current optical disks by using
conventional technologies [1, 2]. Optical storage based on FODs for archival application is currently
being developed at NHK STRL.

2. Concept of archival storage using FODs
Some large-capacity storage systems using FODs have been reported [3, 4]. These systems, however,
have two problems: low recording speed and excessive size for broadcast applications. To solve theseproblems and achieve tape-media-equivalent performance, we have devised a new concept of storage
based on FODs, namely, “flexible-optical-disk archival storage” (FOD-AS) as shown in Fig. 2. PluralFODs stored in the palm-sized cartridge are simultaneously written or read by plural drives in thesystem the size of a current broadcast-use VTR [5, 6]. This storage system achieves superior
performance compared to LTO systems and the potential for performance improvement in the future.
Figure 3 shows the example of the roadmap for FOD-AS. As for the future, the introduction of advanced
technologies such as multi-layer recording and high-speed disk rotation promises larger capacity andhigher data transfer rate. FOD-AS is expected to be widely used beyond broadcast-use archival
application.

3. Prototype of FOD-AS
The specifications of the FOD-AS prototype are listed in Table 1. The three key technical components
for creating a FOD-AS, namely, FOD cartridge, compact FOD drive, and carriage mechanism for FODs,
are described as follows.
(i) Palm-sized cartridge
Figure 4 shows the prototype of the FOD cartridge with a height of about 6 cm, which is composed often trays, each containing ten FODs with a 25-GB-capacity recording layer. The cartridge can therefore
store one hundred FODs, giving total capacity of 2.5 TB. In other words, one tray has a capacity of 250
GB, which is equivalent to that of the cassette for a broadcast-use VTR (HD-D5).
(ii) Compact FOD drive
Figure 5 shows the prototype of the compact FOD drive and its configuration. A stabilizing
mechanism is indispensable for stable rotation of the FODs because of their flexibility [2]. The new
configuration makes the FOD drive almost the same size as current optical disk drives because the tray
for housing the FODs also functions as a stabilizing mechanism. Each FOD is loaded into the drive with
its recording layer upward. Each one can rotate without any contact by forming an air film of a few
hundred micrometers between the tray and the FOD. An optical head is positioned above each FOD andwrites data to each one. HDTV video (MPEG2 at 100 Mbps) recording confirmed the stable operation of
the prototype FOD drive (Fig. 6).
(iii) Carriage mechanism for FODs and FOD-AS
Figure 7 shows an FOD-AS prototype, which can be installed in a 19-inch wide rack like a current
broadcast-use VTR. The FOD-AS is composed of a cartridge, ten FOD drives (a pair of drives in fivetiers), and the carriage mechanism for transporting the FODs. One tray is pulled out from a cartridge, andeach of the ten FODs stored in the cartridge is distributed to one of ten FOD drives by rotating andlowering arms which have an air-adsorption mechanism to absorb air onto the inner unrecorded area of
the FODs. The distributed FODs are collected in reverse order of distribution. The carriage mechanism
for transporting the FODs worked stably and quickly when DVD drives were used in place of FOD drives.

FOD-AS is expected to achieve a data-transfer rate of more than 1 Gbps using parallel recording.

4. Conclusion
An archival storage system using flexible optical disks—called “flexible-optical-disk archival storage”(FOD-AS)—that provides terabyte capacity at gigabits/s data-transfer rate was proposed. FOD-AS isexpected to be put to practical use for archival storage at broadcast stations in the near future because ofits merits of random accessibility, long-life data-storage capability, and long intervals between
data-migration operations for archival storage. Thanks to its high performance, FOD-AS is also
applicable to other archival applications such as a data-center storage.

References[1] D. Koide, Y. Takano, H. Tokumaru, N. Onagi, Y. Aman, S. Murata, Y. Sugimoto, and K. Ohishi: Jpn.
J. Appl. Phys., Vol. 47, No. 7 (2008) 5827.
[2] D. Koide, Y. Takano, H. Tokumaru, N. Onagi, Y. Aman, S. Murata, Y. Sugimoto, and K. Ohishi: Jpn.
J. Appl. Phys., Vol. 49, No. 8 (2010) 08KC05.
[3] T. Yoshida, T. Shimizu, I. Naniwa, Y. Abe, K. Yoshida, K. Sato, H. Awano, H. Ido, T. Iida, Y.
Watanabe, H. Kishi, A. Inaba, M. Tani, H. Yamanaka, S. Osawa, M. Yoshihiro, and N. Ota: ISOM 2007
Technical Digest Mo-C-02 (2006).
[4] T. Iwanaga, M. Akiyama, M. Kubota, and S. Ohkubo: ISOM 2009 Technical Digest (2009) We-H-06.
[5] ISOM Optical Memory Application Roadmap Report, ISOM secretariat, Adthree Publishing Co. Ltd.
(2009).
[6] D. Koide, T. Kajiyama, H. Tokumaru, Y. Takano, N. Onagi and K. Tsukahara: ISOM 2010 TechnicalDigest (2010) Th-PO-03.

800
700

5000

600
4000

500

Programs
3000
2000

400

News

300
NHK TV program libraryin 1981200

1000

NHK Archives open in 2003

plural FODs

Programs (thousands)

News items (thousands)

6000

cartridge

parallel write/read01985

1990

1995

2000

2005

archival
data

10001980

plural drives

2010

2015

Year

Fig. 1. Transition of news and program contents

Fig. 2. Concept for flexible-optical-disk

preserved at NHK

archival storage (FOD-AS)

Table 1. FOD-AS specifications

MediaCartridge

wavelength/NA

405 nm/0.85

number of drives

10FOD-X
next-generation
technologies（SIL, etc.）

capacity

25 GB

type

write-oncediameter/thickness

120 mm/0.1–0.2 mm

total capacity

2.5 TB

number of FODs

100

FOD-3
（10 TB/3.6 Gbps）
100 GB/20,000 rpm

Capacity

Drive

dimensions (H×W×D) 58.5 × 136 × 147.5 mm
Dimensions 500(H) × 420(W) ×700(D) mm

FOD-2（5 TB/2.7 Gbps）
50 GB/15,000 rpm
FOD-1（2.5 TB/1.8 Gbps）
25 GB/10,000 rpm
Data-transfer-rate

10 disks/tray

Fig. 3. Example of FOD-AS roadmap in the caseof 100 disks/cartridge and 10 drives/unit

10 trays(100 disks)Fig. 4. FOD cartridge (2.5-TB capacity)

FOD drive

optical headspindle motor

FOD

Fig. 6. Playback HDTV video
stabilizing & loading mechanism for FOD

Fig. 5. Compact FOD drive

cartridge

carriage mechanism for FODs

Fig. 7. FOD-AS prototype

10 drives(2 drives × 5 tiers)