I'm watching geth 1.4.17 on Activity Monitor.
Judging by the Network page, it's not doing anything. Rcvd Bytes is 5.9MBytes, and Sent Bytes is 2.6MBytes, and it's been that way for a while now.
But on the Disk page, Bytes Written is 4.66GBytes, and Bytes Read is 5.17GBytes, and both are increasing at about 4-6MBytes/sec.
What, precisely, is geth doing here?