Other factors may heighten this disparity between workloads even further, Wachs said. For instance, disk caching may eliminate the need to access the disk at all. In cases where caching is used, the customer may actually be severely overcharged. Also, excessive metadata lookups to find the appropriate data location may consume an inordinate amount of resources.
"This is an unsustainable approach because either the client or the provider will be unhappy," Wachs said. "The clients with the easy requests will pay too much and the clients with the difficult requests will pay too little."
Wachs suggested an alternative billing mechanism, one based on disk time, or the amount of time it actually takes the disk to read or write the material.
"When we charge for disk time, and chose a rate for disk time that matches the cost for the provider, the costs are being recovered fairly," Wachs said.
Attendees brought up various issues with this approach. One noted that clients may be willing to pay a bit more overall to get a more predictable and easily understandable bill, mentioning as an example how the cellular phone industry charges on a simple flat rate and per-minute basis rather than how much the actual cell phone towers are used by each customer.
Wachs countered that the disparity between the costs of running a cloud service and what is being charged can be a significant difference, and not just a subtle averaging of the costs.
Cell phone customers probably "aren't losing sleep over whether they are paying $40 a month instead of $30 a month," he said. Businesses that are paying $40 million a month rather than $30 million a month, on the other hand, may want "the accounting and pricing to be a lot closer to the actual cost," he said.
Andrew Warfield, the session chairman for the economics track that Wachs' talk was part of, noted that the presentation was one aspect of a larger challenge now being faced by cloud providers, namely the task of examining current operational practices in a deeper, more complex way in order to offer simpler, less expensive services to their customers.
Existing cloud storage metrics "are appealing from a customer-facing standpoint as the right way to market the whole system," Wachs said. "But you need to have something in the long term that will actually match the cost for the provider," he said.
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