Signal Capture and Archive Systems
Today, information takes on many forms. Digital and analog mediums provide valuable data that can be used to support analysis, generate revenue, provide unmatched distribution capabilities, and preserve content for years to come. Building systems to capture, store and distribute this information requires a careful look at the unique aspects of the signal being stored, the expectations of the user, and the application environment.
The variety of information being acquired has a dramatic impact on the information systems used to create, store, and share this data. Traditionally, RAID systems and tape drives or tape libraries have supported the bulk of information capture, storage distribution, and archive functions. In recent years, the CD and DVD have made some inroads as alternative mediums for distribution and archive. Each of these mediums has a place in the properly designed capture and archive system. Each offers valuable characteristics at some stage of the data life cycle and the best storage system makes use of the strength of each of these mediums.
Before deciding on the best media to use to store information, the problem of gathering the information in a usable digital format must be overcome.
Collecting and Converting the Data
When designing a signal storage and archive system, we categorize information sources in three general classes:
File – material supplied through a server or network connection
Hardcopy – physical source medium, typically in the form of a tape cartridge or removable disk (CD/DVD)
Signal – specialized digital information from an instrumentation device or other electronic signal source
Each information source will have its own playback or “playout” device. These devices help to form the overall requirements of the system and are an integral part of any archive, disaster recovery, or distribution requirements of the system.
Files are the most readily accessible information sources. Typically, this information conforms to a known format and complies with the required characteristics of any operating systems or network protocols of the storage environment. Practically speaking, all forms of ingest are designed to convert information into this “computer-friendly” file format.
Hardcopy capture usually involves the use of a conversion device to create a recognizable digital format from the source material. The hardcopy source, the intended end-use of the digital information, the amount of data to be stored, and any distribution criteria all effect the selected conversion method for hardcopy information. Consideration of hardcopy output requirements must also be considered when selecting a hardcopy capture interface to the system.
The source of signal information can vary from a prerecorded tape or disk to live signal information that might be input from a satellite receiver. Signal information is largely characterized by its speed, file format, and the analysis tools that will be used to review the data.
Once the characteristics of the source material are understood, the system components can be selected to effectively capture, store, and distribute the data. The conversion and preservation of these different information sources serves many purposes. For the archivist, a digital copy ensures the integrity and availability of the information for long term access and study. From a business perspective, digital data can be made available for use in revenue generating activities without running the risk of damage to a fragile original. For the IT administrator, a digital file is a familiar element that can be managed as part of an overall IT infrastructure.
Designing the Storage Element
The design of the storage component or content archive is driven by two factors; the ability to effectively create digital data from the source devices and the storage medium used to retain the data. The previous section described some of the basics of the capture and conversion process. At the center of the system is a storage device designed to support the unique requirements of each device.
The important thing to remember when designing the core storage elements is that not all mediums are ideal for all applications. For example, disk drives are ideally suited for fast access and retrieval speeds but not necessarily good for distribution or archive. Therefore, it is imprtant to consider the requirments on storage and playback when selecting a medium. A properly designed storage system will make use of all available storage mediums to best meet the needs and expectations of the user. Table 1 lists and describes some of the important features that need to be identified in order to select the proper mix of storage devices for the storage core.
Table 1. Media Selection Criteria
| Consider |
Understand |
| Speed |
Speed of the input signal
Retrieval speed (user, playout) |
| Capacity |
Capture demands (see below for notes on compression)
Growth demands |
| Access Profile |
Number of users
Allowable time to data
Search and rertival tools |
| Disaster Recovery |
System redundancy
Off-site storage and archive |
| Distribution |
Local/remote system access
Media format for external system access |
About the medium
Disk storage continues to grow as a popular medium for data archives. Disks, like tapes, are magnetic medium and therefore subject to degradation over time. The average disk will provide reliable access to data for 3 to 7 years. The disk will then have to be replaced. A Redundant Array of Independent Drive (RAID) system can reduce the risk of inaccessible data, but the individual drives still have a limited data life thus ultimately increasing overall cost of ownership.
Tape is a low cost medium with increasing performance and capacity points. The medium is ideally suited for backup and distribution applications but carries some inherent risk when used as an archive medium. The laws of physics continuously work against tape over time. Aging and environmental conditions all combine to slowly degrade the recoverability of information from this fragile medium. For all of its positive qualities, tape is not an archival medium. Many tapes made thirty years ago are barely playable today. Although there are some unknowns in qualifying modern tape technology, many experts believe well cared for tapes may last 15 years. Tape, however, is not the only problem. The equipment used to play the tape and the use of multi-generation copies easily adds to the degradation of the content.
Optical media is available in rewritable or write once versions and is capable of offering long term access to the data files. Optical disks are a highly stable storage media that are not effected by magnetic fields, head and media wear, or temperature variations and offers a minimum of 30 years of shelf life. As a distribution medium, CD and DVD offer advantages over all magnetic mediums and are compatible with a wide range of consumer products for playback.
Once all of the capture and storage decisions have been made, the method for managing the digital files as an archive can begin. Practically, the archive represents not only a strategy for long term storage of material but for the long-term access of this material as well.
A note on compression
One method commonly used to reduce the capacity needs of video storage applications is data compression. There are several data compression standards currently in use today and many are driven by the hardware associated with the hardcopy conversion equipment. Compression ratios effect the quality of the stored video and also have a significant impact on the amount of storage that will be required. The basis for determining storage requirements derives from the size of 1 second of uncompressed NTSC video:
30 frames per second * 720 pixels wide * 486 pixels high * 2 bytes per pixel = 20,995,200 bytes
The value of 2 bytes per pixel is derived from the M-JPEG A standard of JPEG compression which uses YUV 4:2:2 video. In 4 pixels of video, there are 4 bytes of Y, 2 bytes of U, and 2 bytes of V, for a total of 8 bytes for every 4 pixels, i.e. 2 bytes per pixel.
The storage calculations must also include audio. Therefore, to include 44 kHz, 16 bit, stereo audio:
44,000 audio samples per second * 2 bytes per sample * 2 samples for stereo = 176,000 bytesThus the total size for 1 second of uncompressed NTSC video with CD quality stereo audio is:
20,995,200 bytes/second (Video) + 176,000 bytes/second (Audio) = 21,171,200 bytes/second.The calculations in Table 2 use a rounded 21 MB/second raw video transfer rate with compression to calculate a basic media transfer rate and storage time. For reference, MPEG-2 represents about a 40:1 compression ratio.
Table 2 The Effects of Compression in Storage Capacity
| MB/sec |
Compression Ratio |
Minutes/GB |
Hours/TB |
| 0.21 |
100:1 |
79.3 |
1320 |
| 0.5 |
42:1 |
34.7 |
580 |
| 1 |
21:1 |
16.67 |
280 |
| 2 |
10:1 |
8.33 |
140 |
| 4 |
5:1 |
4.17 |
70 |
| 6 |
3:1 |
2.78 |
50 |
| 8 |
2.6:1 |
2.08 |
30 |
| 9 |
2.3:1 |
1.85 |
30 |
| 10 |
2.1:1 |
1.67 |
30 |
| 10 |
1.7:1 |
1.39 |
20 |
| 13.4 |
1.6:1 |
1.24 |
20 |
| 21 |
1:1 |
.79 |
10 |
A True Archive Solution
Rising Edge Technologies works with its customers to provide all the elements required to create a comprehensive signal capture, storage and distribution system. These systems overcome many of the limitations of generic storage solutions by making data readily accessible in the format demanded by the application environment.
These systems support the needs of the IT department by offering a direct or network attached appliance-style product utilizing disk, tape and optical media in a function-appropriate format. Disk can be selected for performance while optical might be selected for enhanced media life and durability. High capacity robotic media exchange systems are also available for on-line access to large volumes of data. The network-attached features of this archive make it easy to support access and retrieval of data for the production and distribution of information.
Solutions for signal capture
Recorded or instrumentation style signals can be captured and stored using Rising Edge Technologies DR product family in conjunction with a central storage system. Once the signal is on the recorder, analysis can proceed either through the output ports of the recorder or using a built in File Transfer Protocol (FTP) function. The FTP function supports full bi-directional data transfer to and from the recorder. Using FTP, file transfers occur in a format compatible with the requesting host computer. The FTP function also enables any DR product to transfer data to any Rising Edge storage system. Unlike traditional capture applications that move data out of the system to be exposed to harsh environmental conditions or loss, these systems keep all of the data available and accessible within seconds of a user request.
Typically, data is stored by the recorder and only archived after it has been analyzed. The DR family of recorders offers features and functions that can support pre- and post- analysis archival operations. The DR family utilizes removable media carriers to facilitate extended recording, data transport and exchange, or physical archive of the media pack.
Solutions for multimedia applications
These integrated solutions support the collection of multimedia data from VCRs, cameras, or a variety of analog and digital sources through Rising Edge Technologies VC10000. The VC10000 comes standard with a Win2K server and a Pinnacle Systems Capture card supporting MPEG-2 video files. Pinnacle Systems products are the latest, top of the line solutions for real-time results in video editing and the creation and finishing of streaming video. The VC10000 feeds a 2 TB QuickVault RAID array to create a high capacity data storage unit with the highest record speeds possible.
This capture component can be coupled to disk, tape or a DVD library. With DVD technology, users can directly access a specific segment of the disc for immediate playback or editing without time-consuming task of fast-forwarding or rewinding. DVD discs provide more than 100,000 write/rewrite cycles and a data life of more than 30 years. The quality of audio and video stored on DVD doesn’t deteriorate with repeated playback, doesn’t require special handling, and doesn’t fade over time as it does in a tape archive. The archival component is scaleable and features optional data mirroring and tape back up support for all of your digital media assets.
Summary
This paper presents a high level overview of some of the issues to consider when designing a signal storage system and selecting appropriate storage technologies. Rising Edge Technologies components and systems can be used as a key piece in meeting the goals of these applications. Each of the topics presented must be considered in relationship to the type of applications the archive will support, level of user interaction with the media, workflow considerations, and performance demands. Visit the Companies web site for more white papers regarding the capture and storage of data or contact the company directly to request more information.
|
