Tried starting up mongo with:
mongod --oplogSize 5000
However the oplog never grows beyond about 1GB.
Despite specifying the flag the log file writes:
Sun Feb 13 18:45:13 MongoDB starting : pid=824 port=27017 dbpath=d:\DB\Mongo\data 64-bit
Sun Feb 13 18:45:13 db version v1.6.5, pdfile version 4.5
Sun Feb 13 18:45:13 git version: 0eb017e9b2828155a67c5612183337b89e12e291
Sun Feb 13 18:45:13 sys info: windows (6, 1, 7600, 2, '') BOOST_LIB_VERSION=1_42
Sun Feb 13 18:45:13 [initandlisten] waiting for connections on port 27017
Sun Feb 13 18:45:13 [initandlisten] ******
Sun Feb 13 18:45:13 [initandlisten] creating replication oplog of size: 904MB... (use --oplogSize to change)
Sun Feb 13 18:45:13 [initandlisten] ******