Did you read Bianca's paper? I'm not sure how you can ignore the evidence of non-Poisson distributions to maintain your claim that "failures are still a Poisson process"...
Also, it's *very* likely that vintage is correlated with temperature. Servers built in 2001 are very likely to have different thermal characteristics (e.g., different airflow, layout, and thus disk drive temperatures). On top of that, the power consumption of disk drives has increased meaningfully over that time period, so that a 2001 5400rpm drive very likely runs cooler than a new 7200rpm drive.
Well, actually, Bianca's paper at the same conference showed that even though everyone assumes a Poisson distribution that's not what disk drives actually do...see Figure 5. I have no idea whether Google's population is similar (the data in Bianca's paper is partly from SCSI drives) but what both papers say is that the vintage effect is very pronounced, which suggests that the distribution doesn't look fishy, if you pardon the pun.
I think you bought the CO's story a bit too quickly. The real story goes something like this: under the standard tax rules, if Google invested $600M or so in NC they would pay $300M (!) in taxes. They got a $250M rebate so now they pay $50M. You didn't see similar stories about their Oregon datacenter because most of the taxes that were discounted in NC don't exist to begin with in OR. For example, in NC you have to pay (as a company) something called "personal property tax", plus there's sales tax, and in OR neither of these exist.
Disclaimer: I'm neither a lawyer nor a tax accountant, but I know one;-)
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Did you read Bianca's paper? I'm not sure how you can ignore the evidence of non-Poisson distributions to maintain your claim that "failures are still a Poisson process"... Also, it's *very* likely that vintage is correlated with temperature. Servers built in 2001 are very likely to have different thermal characteristics (e.g., different airflow, layout, and thus disk drive temperatures). On top of that, the power consumption of disk drives has increased meaningfully over that time period, so that a 2001 5400rpm drive very likely runs cooler than a new 7200rpm drive.
Well, actually, Bianca's paper at the same conference showed that even though everyone assumes a Poisson distribution that's not what disk drives actually do...see Figure 5. I have no idea whether Google's population is similar (the data in Bianca's paper is partly from SCSI drives) but what both papers say is that the vintage effect is very pronounced, which suggests that the distribution doesn't look fishy, if you pardon the pun.
I think you bought the CO's story a bit too quickly. The real story goes something like this: under the standard tax rules, if Google invested $600M or so in NC they would pay $300M (!) in taxes. They got a $250M rebate so now they pay $50M. You didn't see similar stories about their Oregon datacenter because most of the taxes that were discounted in NC don't exist to begin with in OR. For example, in NC you have to pay (as a company) something called "personal property tax", plus there's sales tax, and in OR neither of these exist. Disclaimer: I'm neither a lawyer nor a tax accountant, but I know one ;-)