NOTE: the multiplication factors below are not calibrated yet...these
are chosen based on approximations for now. For reference purposes,
assume each disk on a server can have a sustained I/O throughput of
100 MBytes/sec. Suppose there is an array of 16 disks per server..theoretically
one could get 1.6GBytes/sec. Suppose network speed is 1GBit/sec which is
128MBytes/sec, although actual transfer rate over the network may be lower.
We are only concerned with relative costs, not absolute values.
For relative costing, let's assume sending data over the network is
about 16x slower than reading/writing to an array of local disks.