Broadcast archives
Jul 1, 2009 12:00 PM, By David Austerberyy
Can storage keep up with an ever-growing amount of produced content?
Partial restore
This is often cited as a differentiator between video storage and generic IT systems. First-generation LTO had a transfer rate around 15MB/s. A one-hour program stored as 50Mb/s MPEG is about 20GB. Restoring files from a tape archive takes about 20 minutes. If you needed a three-minute clip for a promo, tying up a tape drive for 20 minutes was not efficient. With LTO-4 offering 120MB/s transfer rate, it's not such an issue. The entire program can be restored to disk. If a promo is being made, it will be aired in the near future anyway and will have to be restored from tape in its entirety.
Partial restore is still a valid concept for large HD files. These may be stored at 200Mb/s or higher, and a 120-minute movie is a large file to store even for two weeks on the disk array. A similar reasoning can be applied to HD sports content. Once the game has been aired, all that may be required in the future are highlights; partial restore is ideal for such applications. The move to 3GB/s, even with mezzanine compression, only exacerbates the issue.
The medium
Although many technologies from the mundane to esoteric have promised replacements for magnetic storage, they remain just around the corner. Optical storage is still limited to 50GB per disk, so the conventional disk drive and data tape remain at the heart of any storage subsystem. Solid-state drives are finding applications in acquisition and playout, but it is still in the early days for mass storage.
Tape libraries come in all sizes, from an auto-loader with a capacity of 10 tapes up to enterprise libraries with capacities of tens of thousands of slots.
The front end of an archive today is a disk array. This technology has evolved from parallel-connected disks, SCSI and IDE/ATA to the current serial technology, SAS and SATA. A RAID subsystem can provide backup against disk failure. These arrays provide cost-effective storage for work in progress and smaller archives.
For longer-term and low-cost storage, data tape is the most popular option. Again, the technology is constantly changing and improving. Technologies like DLT have been replaced with LTO. The next-generation LTO-5 stores 1.6TB, about 70 hours of 50Mb/s video. The LTO cartridge is about two-thirds the volume of 3.5in hard drive, so the storage density is about double (a 1TB drive). Hard drives need more space around them for cooling and disk controllers, so with current technology, the tape store will take up less floor space.
Energy efficiency
Energy use has always been a cost factor with archives. Videotape and film both need climate control. For a long-term tape archive, the U.S. Library of Congress recommends 10 degrees Celsius and 20 percent to 30 percent relative humidity (RH). For film, it recommends 3 degrees Celsius and 20 percent to 30 percent RH.
Spinning disks draw power, so they need additional cooling. For a deep archive, why keep the disks spinning when they are not in use? This is the principal behind a massive array of idle disks (MAID). Unused disks spin down until they are needed. In a typical MAID array, only 25 percent of the disks are spinning. Not only does it reduce power consumption, but also it prolongs the life of the drives.
Data tape libraries use power for the robots and drives, but far less than an equivalent capacity disk array. The data tape has the same environmental requirements as the videotape, not too hot or humid.
You can prove anything with statistics, but the generally held view is that tape is the lowest energy user.
Summary
An archive can serve several functions. It can form part of the backup strategy, it can be used for DR, just as a program repository, or all three.
The archive may be thought of as a permanent store, but the underlying technology is anything but permanent. There is no right answer to archive design. No current storage technology has a long life. Drives become obsolete, and the recording media decays. The current wisdom is to replace drives every three to five years, and to migrate data from tapes after 10 to 15 years. These factors must be considered when calculating the operating costs of the archive. Protecting the archive, automated monitoring and migration of drives, and media condition are just not possible with videotape.
Archive management has become a service to an overall DAM/MAM system, which handles data movement, transcoding and tape management. For the broadcaster, this can deliver large cost savings. The traditional broadcaster uses manual processes to move content from production to transmission. The move to file-based workflows can eliminate the bulk of those human processes.
There are choices for the broadcaster: The complexity of managing the archive can be outsourced to a data center. This could be within the corporate firewall or at a remote shared data center.
Each broadcaster has a different set of technical requirements and will place its own value on its assets. Storage technology is getting cheaper, but production creates ever more content. New formats like HD, 2K and 4K plus UHDTV in the future just increase the file sizes for a given program duration. Today's optimum solution will be wrong in two years. So choose something, and expect to migrate!
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