Storage in the broadcast environment

By Eric Dufosse, Thomson Broadcast & Media Solutions

Review contents:

Data storage systems for TV Application technology of the uniform disk arrays from Avid Technology Decisions of Ehance Tech company SANStream from Huge Systems DriveBox from JC System Integration VelocityQ and Storage Area Networks (SAN) Network decisions from Medea Palladium architecture SAN/NAS decisions from Raidtec Network storage decisions of Sanbolic Company Storage in the broadcast environment

There are two points to be made above all others when considering storage strategies for broadcast systems: there are no good or bad storage systems, just solutions which are appropriate to a particular installation; and in defining your solution, remember that the requirements of television are very different than any IT application.

Let’s address these points in reverse order, as a simple illustration will show the differences between a network of video servers and those of standard IT drives and components.

A typical IT application requiring storage in the terabyte region is generally transactional. These applications, found in banks, large-enterprise customer service centres, or airline reservation services, generally support non-concurrent access to small files and a high number of parallel-access demands.

In video facilities, by contrast, there are relatively few numbers of concurrent users, but there is the potential for multiple simultaneous access demands to very large files. These demands must be met without compromising extremely challenging quality of service considerations -there can be no chance for dropped video frames, hard drive latency or delay, bandwidth overload, or component failure that could prevent the airing of a programme or commercial.

For that reason it is vital that the architect of a server network understands the special demands of video as well as of servers. To that end, Thomson has invested substantial research and development resources to create a range of networked solutions to meet all requirements, so users can choose the solutions that best fit their environment.

Video networks through the eyes of a news system

So under what circumstances would you deploy networked video storage? The most common application is in television news, where a management infrastructure such as the Grass Valley Digital News Production (DNP) solution from Thomson manages the entire production workflow getting stories to air as quickly as possible.

In a news application, raw material enters the system, perhaps as a live feed, as rushes from a crew on location, or as a cut story from a remote site. Once in the DNP system, a number of news professionals will access the material to create the final story.

Even if a story comes in as a finished package it will need to be available to many people simultaneously. A news controller will review it for content and the programme director will check it for timing; the graphics department will add captions and other illustrations; and an editor may need to cut a teaser from the main story.

But typically in a news workflow, material is ingested in raw form to be edited into a number of forms for different programmes either using desktop tools, craft edit workstations, or both. A story also needs captions and graphics, checking for content and timing, and so on. All of this happens under extreme deadline pressure.

In this environment, a high-capacity, fast and reliable video network is crucial: even the smallest delay can be the difference between being first to air with a late-breaking story or not.

During news transmission, a video network may also have to deliver stories, perhaps even conforming edits on the fly at the time of broadcast. This task has to take the top priority, and no user will tolerate anything other than frame-accurate delivery, a definition of real-time performance that is far more demanding than anything in the wider IT world.

SAN systems: unmatched performance for large installations

The accepted wisdom has been that, to achieve the standard of frame-accurate delivery 24 hours a day, 365 days a year, facilities need a storage area network (SAN), built around RAID 3 drives and fibre channel networking for speed and resilience. Certainly this approach is preferable for large-scale, high profile installations.

SAN Nero

Yet even this kind of SAN is not sufficiently rigorous for real-world applications such as digital news production. That’s because the real challenge is ensuring that the video network can maintain broadcast-quality performance right up to its capacity, without losing a single byte — doing so in a completely reliable manner.

The hardest part of this challenge lies is in providing the redundancy necessary to offer complete protection against the failure of any component without any disruption of service. That’s why Thomson design engineers spend a significant amount of time defining the worst-case scenarios a SAN could encounter and then configure a solution that provides resilience against them. They achieve this by qualifying the right components to form the network, and by creating the hardware and software elements for full redundancy.

The result is the Grass Valley Open SAN, part of the Grass Valley DNP offering, the first in the industry to meet this extremely rigorous specification, with the ability to maintain full broadcast-quality output while rebuilding data. There are now more than 200 digital newsrooms and transmission systems which rely on the Open SAN system, including CNBC, MBC jingu, HBO, WABC, Network 10 Australia, Eurosport, Sogecable

NAS systems: reliable, cost-effective option for small facilities

While this kind of SAN configuration is the preferred route for large-scale, high profile installations, today’s small- and mid-sized broadcasters are also seeking an equally resilient, cost-effective solution. That’s why Thomson developed a network attached storage (NAS) configuration that uses many of the same components of the SAN system.

At the heart of both SAN and NAS systems is the same storage: RAID arrays of disks linked by fibre channel running under the custom-designed Grass Valley Cohera common storage architecture. In a NAS configuration, these drive arrays are attached to a production network using gigabit Ethernet connectivity.

To challenge the myth that NAS-based storage is inherently less reliable under pressure, Thomson developed the Grass Valley NewsShare quality of service technology to provide deterministic server and client channel bandwidth, which is critical to ensuring smooth workflow. Blending the NewsShare technology with the off-the-shelf technologies of the NAS system creates a highly affordable storage option. Like the SAN system the Grass Valley NAS system is in commercial use at a number of sites, including, GloboSat, Network 7, TV amazona, Flevoland TV, Network 7 Australia and I Vision.

Stretching capital budgets further, Thomson can implement NewsShare NAS technology on an array of serial ATA (SATA) drives rather than fibre channel SCSI drives. SATA drives offer lower cost per unit — though very different performance characteristics — than SCSI drives.

Making the right choice

When discussing a digital newsroom, Thomson specialists spend a long time understanding the requirements and calculating the required bandwidth, so that a system meets the capacity requirements for the present, and can support likely future growth.

So which is right for you?

In general, a SAN approach works best for applications involving large numbers of streams. The Grass Valley Open SAN supports 64 streams, each up to 50 Mb/s for standard-definition (SD) signals or 80 Mb/s for high-definition (HD) signals, and provides unmatched reliability. The Grass Valley NAS system offers an affordable option for smaller networks — up to 30 SD streams — while maintaining a guaranteed quality of service and providing gigabit Ethernet connectivity for easy integration into existing networks.

For more cost-sensitive applications, the Grass Valley NAS system can support an array of SATA drives. While these drives are more limited in their bandwidth and concurrent-user support capabilities compared to SCSI drives, they can provide a perfect entry point for digital production techniques in smaller newsrooms — and can support the optional expansion to a SCSI-based NAS or SAN in the future.

Indeed any Grass Valley DNP storage system can be expanded at any time without changing workflows or disrupting an operation. It’s simply impractical to take a news operation off the air for days at a time while storage systems are rebuilt.

So SAN or NAS? In the end, the answer is that, provided the system architecture is developed with the specific challenges of the broadcast video server in mind, there are plenty of options available to meet the performance and capital needs of all facilities.

Material provided by Thomson Broadcast & Media Solutions Company