Now that the oplog is created during rs initialization I suspect the command line/config option no longer works as expected.

mongod --replSet test --oplogSize 10 --port 2002 --dbpath /tmp/rs2

mongod --replSet test --oplogSize 20 --port 2002 --dbpath /tmp/rs2

Here are the results after the two restarts.

Mon Feb 21 22:45:31 trying reconnect to 127.0.0.1:2002
Mon Feb 21 22:45:31 reconnect 127.0.0.1:2002 ok
test:SECONDARY> db.getReplicationInfo()
{
"logSizeMB" : 10,
"usedMB" : 0.01,
"timeDiff" : 86,
"timeDiffHours" : 0.02,
"tFirst" : "Mon Feb 21 2011 22:39:31 GMT-0800 (PST)",
"tLast" : "Mon Feb 21 2011 22:40:57 GMT-0800 (PST)",
"now" : "Mon Feb 21 2011 22:45:33 GMT-0800 (PST)"
}
test:SECONDARY> db.getMongo()
connection to 127.0.0.1:2002
test:SECONDARY> db.getReplicationInfo()
{
"logSizeMB" : 10,
"usedMB" : 0.01,
"timeDiff" : 86,
"timeDiffHours" : 0.02,
"tFirst" : "Mon Feb 21 2011 22:39:31 GMT-0800 (PST)",
"tLast" : "Mon Feb 21 2011 22:40:57 GMT-0800 (PST)",
"now" : "Mon Feb 21 2011 22:45:58 GMT-0800 (PST)"
}
test:SECONDARY>