Deployment:
Several shards, every shard is a replication set made up of at least 3 nodes(1 PRI 2+ SEC)

Problem:
mongodump occasionally produces incomplete dump.

1. -----------------------------------------
2. ----- INCOMPLETE DUMP -----
3. -----------------------------------------
   ubuntu@forest1:/storage/mongodb-dump/2015-11-16/ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht$ mongodump --port=27020 -d ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht -c _Installation
   connected to: 127.0.0.1:27020
   2015-11-17T17:27:32.257+0800 DATABASE: ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht to dump/ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht
   2015-11-17T17:27:32.262+0800 ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht._Installation to dump/ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht/_Installation.bson
   2015-11-17T17:27:44.460+0800 102 documents
   2015-11-17T17:27:44.466+0800 Metadata for ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht._Installation to dump/ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht/_Installation.metadata.json

1. ------------------------------------------
2. ----- DO A COUNT QUERY -----
3. ------------------------------------------
   ubuntu@forest1:/storage/mongodb-dump/2015-11-16/ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht$ export LC_ALL=C
   ubuntu@forest1:/storage/mongodb-dump/2015-11-16/ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht$ mongo
   MongoDB shell version: 2.6.11
   connecting to: test
   2015-11-17T17:29:23.579+0800 warning: Failed to connect to 127.0.0.1:27017, reason: errno:111 Connection refused
   2015-11-17T17:29:23.580+0800 Error: couldn't connect to server 127.0.0.1:27017 (127.0.0.1), connection attempt failed at src/mongo/shell/mongo.js:146
   exception: connect failed
   ubuntu@forest1:/storage/mongodb-dump/2015-11-16/ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht$ mongo --port=27020
   MongoDB shell version: 2.6.11
   connecting to: 127.0.0.1:27020/test
   mongos> use ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht
   switched to db ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht
   mongos> db.getCollection('_Installation').count()
   2971314
   mongos>
   bye

1. --------------------------------------------------
2. ----- NOW DUMPS CORRECTLY -----
3. --------------------------------------------------
   ubuntu@forest1:/storage/mongodb-dump/2015-11-16/ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht$ mongodump --port=27020 -d ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht -c _Installation
   connected to: 127.0.0.1:27020
   2015-11-17T17:30:16.882+0800 DATABASE: ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht to dump/ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht
   2015-11-17T17:30:16.898+0800 ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht._Installation to dump/ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht/_Installation.bson
   2015-11-17T17:30:20.061+0800 Collection File Writing Progress: 200/2971314 0% (documents)
   2015-11-17T17:30:23.272+0800 Collection File Writing Progress: 73600/2971314 2% (documents)
   2015-11-17T17:30:26.006+0800 Collection File Writing Progress: 178200/2971314 5% (documents)
   2015-11-17T17:30:29.301+0800 Collection File Writing Progress: 312300/2971314 10% (documents)
   2015-11-17T17:30:32.298+0800 Collection File Writing Progress: 440900/2971314 14% (documents)
   2015-11-17T17:30:35.053+0800 Collection File Writing Progress: 551000/2971314 18% (documents)
   ^C

1. -------------------------
2. ----- VERSION -----
3. -------------------------
   ubuntu@forest1:/storage/mongodb-dump/2015-11-16/ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht$ mongodump --version
   version 2.6.11

1. ------------------------------------
2. ----- MAY BE USEFUL -----
3. ------------------------------------
   ubuntu@forest1:/storage/mongodb-dump/2015-11-16/ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht$ export LC_ALL=
   ubuntu@forest1:/storage/mongodb-dump/2015-11-16/ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht$ mongodump --port=27020 -d ahtvf235n6ajehqthifsy0wrhxv5lcin4u9jqa72kei0o6ht -c _Installation
   Failed global initialization: BadValue Invalid or no user locale set. Please ensure LANG and/or LC_* environment variables are set correctly.