^{Democracy & Technology Blog} Data retention would be costly

I surmised here that it would be costly for ISPs to retain customer data pursuant to a new proposal in the House of Representatives, and subsequently came upon a news report from a couple years ago in which industry sources predicted the cost of a similar proposal under consideration in the European Union would be quite large:

For AOL, retaining communications data for one year would add an enormous cost, said de Stempel. “There are huge amounts of data involved. AOL has 329m user sessions a day, and its customers send 597m emails, and we’re just one ISP.” De Stempel said that to save all communications data on its UK customers for just one day would require 100 CDs. “If you multiply that (for a year) it will have an enormous impact on our business.”
Further costs would be incurred because an ISP could not simply hand a whole year’s worth of CDs (36,000 in the case of AOL) over to police or other law enforcement agency when a request was made because, they say, this would be an offence under Regulation of Investigatory Powers Act (RIPA). RIPA says that any requests for communications data has to be proportional. “We’d have to search for a particular piece of data,” said de Stempel.
Clive Feather, an Internet expert at ISP Thus who also gave evidence, said AOL’s figure of 36,000 CDs was if anything an underestimate of the scale of the problem. “This is raw data. If ISPs are retaining data so it can be searched later then it has to be organised and indexed,” said Feather. “And this would all have to be paid for.”
Feather said he had no idea where the government’s estimate of £20m for the whole industry came from. “The cost would be £5m to £6m for us alone,” he added.

The full article can be found here.
The transcript of the testimony is here.