mongodb提供了两个命令来备份（mongodump ）和恢复（mongorestore ）数据库。
1.备份（mongodump ）
用法 ：
[root@web3 3]# mongodump --help
options:
--help                   produce help message
-v [ --verbose ]         be more verbose (include multiple times for more 
verbosity e.g. -vvvvv)
-h [ --host ] arg        mongo host to connect to ("left,right" for pairs)
-d [ --db ] arg          database to use
-c [ --collection ] arg  collection to use (some commands)
-u [ --username ] arg    username
-p [ --password ] arg    password
--dbpath arg             directly access mongod data files in the given path,
instead of connecting to a mongod instance - needs 
to lock the data directory, so cannot be used if a 
mongod is currently accessing the same path
--directoryperdb         if dbpath specified, each db is in a separate 
directory
-o [ --out ] arg (=dump) output directory
例子：
[root@web3 ~]# mongodump -h 192.168.1.111 -d citys -o /backup/mongobak/3
connected to: 192.168.1.103
DATABASE: citys  to     /backup/mongobak/3/citys
citys.building to /backup/mongobak/3/citys/building.bson
13650 objects
citys.system.indexes to /backup/mongobak/3/citys/system.indexes.bson
1 objects
备份出来的数据是二进制的，已经经过压缩。比实际数据库要小很多，我的数据库显示占用了260多M，备份后只有2M。
2.恢复（mongorestore ）
用法：
[root@web3 3]# mongorestore --help
usage: mongorestore [options] [directory or filename to restore from]
options:
--help                  produce help message
-v [ --verbose ]        be more verbose (include multiple times for more 
verbosity e.g. -vvvvv)
-h [ --host ] arg       mongo host to connect to ("left,right" for pairs)
-d [ --db ] arg         database to use
-c [ --collection ] arg collection to use (some commands)
-u [ --username ] arg   username
-p [ --password ] arg   password
--dbpath arg            directly access mongod data files in the given path, 
instead of connecting to a mongod instance - needs to
lock the data directory, so cannot be used if a 
mongod is currently accessing the same path
--directoryperdb        if dbpath specified, each db is in a separate 
directory
--drop                  drop each collection before import
--objcheck              validate object before inserting
--drop参数可以在导入之前把collection先删掉。
例子：
[root@web3 3]# mongorestore -h 127.0.0.1 --directoryperdb /backup/mongobak/3/         
connected to: 127.0.0.1
/backup/mongobak/3/citys/building.bson
going into namespace [citys.building]
13667 objects
/backup/mongobak/3/citys/system.indexes.bson
going into namespace [citys.system.indexes]
1 objects
另外mongodb还提供了mongoexport 和 mongoimport 这两个命令来导出或导入数据，导出的数据是json格式的。也可以实现备份和恢复的功能。
例：
mongoexport -d mixi_top_city_prod -c building_45 -q '{ "uid" : "10832545" }' > mongo_10832545.bson
mongoimport -d mixi_top_city -c building_45 --file mongo_10832545.bson
from :