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February 13, 2014

Blu-ray for Cold Storage – What About Tape?

Tiffany Trader
Facebook cold storage 500x

Last week, Spectra Logic’s Bruce Kornfeld, the company’s Interim CMO, raised an important question: “Can Consumer Technologies Meet the Demands of Commercial Data Storage Applications?”

Kornfield’s post was motivated by Facebook’s recent unveiling of a prototype Blu-ray optical disc library, capable of storing approximately 10,000 discs and 1 petabyte of data in a single cabinet. The approach is the latest example of consumer technologies being deployed for commercial data storage applications.

For a company like Facebook, which must store an enormous number of rarely accessed files, such as backups of photos and videos, power consumption and datacenter floor space are major considerations. In this scenario, near-line media, such as optical disks and tape cartridges are compelling options. Unlike conventional disk arrays, these solutions require very little power when idle, and media costs are significantly lower per GB than disk costs. When he broke the news, Facebook Vice President of Infrastructure Engineering Jay Parikh said the new storage system would cost half as much as Facebook’s current HDD cold storage system and use just one-fifth the power.

Kornfield finds it curious that Facebook made the comparisons to standard commercial-grade disk storage, but the social media company neglected to give equal consideration to tape storage, a long-term storage solution that is known for its scalability and cost-effectiveness as well as having “a proven track record of going the distance in serving commercial data storage environments.”

The Spectra rep points out that tape would be the most cost-effective option. “Excluding the cost of the robot and drives, the raw media costs of using 100GB Blu-ray discs works out to be about $0.41 per gigabyte,” Kornfield states, adding that the figure is multiples higher than an LTO tape storage system, which costs just $0.02 per gigabyte.

He further questions whether a consumer-grade technology can withstand the demands of high-duty cycle data storage applications.

“Over the last 20 years the commercial data storage industry has attempted to commercialize multiple consumer technologies including CD ROM, CD Writeable, DVD writeable, 4mm Digital Audio Tape, 8mm video tape, and VHS video tape – with mixed results,” notes Kornfield.

“Consumer technologies offer high-volume and typically low cost storage media. The ‘low cost’ strengths of these technologies have also led to their downfall as they lack the device robustness and data reliability required by commercial data storage applications. In addition, consumer grade drives and media just don’t last very long. Blu-ray disc drive load mechanisms are probably good to a few thousand load/unload cycles. This compares with an LTO tape drive that is rated to 250,000 load/unload cycles. As you can see – the difference in durability is substantial!”

Facebook execs say the optical media will provide 50 years worth of durability, but the 100GB Blu-Ray discs used in the prototype storage solution have only been around for a couple of years. The 50-year certification is based on accelerated aging techniques that are supposed to emulate 50 years of real time. However, as at least one tech blogger has pointed out, theory and practice don’t always mean the same thing.

In a follow-up blog, Kornfield provides a comprehensive comparison of a Blu-ray system versus an LTO tape library solution, as demonstrated in the chart below:

Spectra Logic Blu-Ray Tape comparison1 465x

A second chart looks at the number of racks (floor space) required and the total media cost for an exabyte-sized Blu-ray disc solution and an exabyte-sized LTO tape library:

Spectra Logic Blu-Ray Tape exabyte comparison 465x

This analysis includes several assumptions, including:

  • The cost of the sheet metal, power, fans and robotics required was assumed to be about equal between tape and Blu-ray.
  • The cost of the media is based on Internet research to find approximate lowest online pricing.
  • The cost of the drives is not included because pricing is so variable depending on the source and in the big picture, the drive cost is dwarfed by the cost of the media.

“While this analysis isn’t exact, even with the assumptions noted above it is very clear that tape is an advantaged media for storing data for long periods of time,” Kornfield writes. “Even if you assume Facebook builds its own racks and negotiates pricing for 100GB media that is closer to the cost of 50GB media – the point remains the same – tape delivers significant advantages in cost, performance and floor space. As far as power consumption goes, tape and Blu-ray are about the same because data is stored on media that doesn’t require constant power.”

Per its usual strategy, Facebook is rolling out the optical storage system one stage at a time, not moving to full production until it’s proven. According to VP Parikh, the first site is already operational and storing 30 petabytes of data. The company plans to implement a second site soon, and within a couple months, expects to have 150 petabytes of data in cold storage. A full-sized facility could hold 3 exabytes of storage space.

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