> rs.initiate({_id: 'test',
... members: [
... {_id: 0, host: 'localhost:27017'},
... {_id: 1, host: 'localhost:27018'},
... {_id: 2, host: 'localhost:27019', arbiterOnly: true}
... ]})
{
"info" : "Config now saved locally. Should come online in about a minute.",
"ok" : 1
}

> rs.conf()
{
"_id" : "test",
"version" : 1,
"members" : [

{ "_id" : 0, "host" : "localhost:27017" }

,

{ "_id" : 1, "host" : "localhost:27018" }

,

{ "_id" : 2, "host" : "localhost:27019", "arbiterOnly" : true }

]
}

> rs.status()
{
"set" : "test",
"date" : "Tue Oct 12 2010 19:00:24 GMT+0400 (MSD)",
"myState" : 1,
"members" : [

{ "_id" : 0, "name" : "Alaz-MBP.local:27017", "health" : 1, "state" : 1, "self" : true }

,

{ "_id" : 1, "name" : "localhost:27018", "health" : 1, "state" : 2, "uptime" : 37, "lastHeartbeat" : "Tue Oct 12 2010 19:00:23 GMT+0400 (MSD)" }

,

{ "_id" : 2, "name" : "localhost:27019", "health" : 1, "state" : 7, "uptime" : 41, "lastHeartbeat" : "Tue Oct 12 2010 19:00:23 GMT+0400 (MSD)", "errmsg" : "." }

],
"ok" : 1
}

*****************

> db.runCommand( { replSetReconfig: {_id: 'test',
... version: 2,
... members: [
... {_id: 0, host: 'localhost:27017'},
... {_id: 1, host: 'localhost:27018'},
... {_id: 2, host: 'localhost:27019', priority: 0}
... ]} })

{ "ok" : 1 }

> rs.conf()
{
"_id" : "test",
"version" : 2,
"members" : [

{ "_id" : 0, "host" : "localhost:27017" }

,

{ "_id" : 1, "host" : "localhost:27018" }

,

{ "_id" : 2, "host" : "localhost:27019", "priority" : 0 }

]
}

> rs.status()
{
"set" : "test",
"date" : "Tue Oct 12 2010 19:02:28 GMT+0400 (MSD)",
"myState" : 1,
"members" : [

{ "_id" : 0, "name" : "Alaz-MBP.local:27017", "health" : 1, "state" : 1, "self" : true }

,

{ "_id" : 1, "name" : "localhost:27018", "health" : 1, "state" : 2, "uptime" : 32, "lastHeartbeat" : "Tue Oct 12 2010 19:02:26 GMT+0400 (MSD)" }

,

{ "_id" : 2, "name" : "localhost:27019", "health" : 1, "state" : 7, "uptime" : 32, "lastHeartbeat" : "Tue Oct 12 2010 19:02:26 GMT+0400 (MSD)", "errmsg" : "." }

],
"ok" : 1
}