The Facebook Prototype: Economics of Blu-ray Disc versus Tape Storage

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Facebook unveiled a prototype display of a Blu-ray optical disc library at the recent Open Compute Project Summit. The Blu-ray prototype contains approximately 10,000 optical discs and a Petabyte of data in a rack-sized cabinet. The system caught our interest at Spectra Logic, and in my last blog I examined the ability of consumer-driven Blu-ray disc technology to handle commercial data storage applications. In this post, we've taken a look at the specs and approximate costs of a Blu-ray system versus an LTO tape library solution and I think the results are noteworthy.

Format Media:

Blu-ray 100 GB disc

LTO 2,500 GB tape Library Solution

Tape Advantage

Cost per GB

$0.41

$0.02

>20x

Storage Capacity per Rack

1,000 TB

2,375 TB

>2x

Media Cost per Rack

$411K

$48K

88% less cost

Transfer Rate per Drive

27MB/sec

160MB/sec

~6x faster

Facebook talked about the need to store an Exabyte of data, so in the table below, we've compared 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:

Format Media:

Blu-ray 100 GB disk

LTO 2,500 GB tape Library Solution

Tape Advantage

Number of Racks per EB

1,000

421

Less than half the floor space

Total Media Cost

$411 Million

$20 Million

95% less cost

Note: This analysis is based on the following assumptions:

  • 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. 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.

And, as I noted in my previous blog post, Blu-ray is a consumer-grade technology and not designed for serious data intensive environments. It is much more likely to incur errors, jammed drives and failed drives than a tape storage system.

Maybe I'm missing some key facts around what caused Facebook to take this approach with their prototype—it might be an interesting discussion to have. Clearly, Facebook has some very smart engineers, but I can't help but wonder why they overlooked tape?