[puzzle]

It was even crazier: when the original download server was written, local disk was faster, mainly because the network wasn't too fast (rack locality was a concern, way back when), but also because GFS chunk servers weren't, either. At the time of the rewrite, Firehose and co. were being deployed everywhere, D did a better job at serving bytes and, later, local disk use was placed in a lower QOS level. Unless you were one of the few teams that had a good rationale for dedicated machines, if you fought for I/O time on a given disk against D, invariably you lost.