Ideas to reclaim some spaces

I have build a shard mongodb cluster in production and each shard having 3 nodes.below is the db stats from one shard.

sd1:PRIMARY> db.stats(1024)

{

        "db" : "aureporting",

        "collections" : 8,

        "objects" : 2070805,

        "avgObjSize" : 4271.989012968386,

        "dataSize" : 8639117,

        "storageSize" : 10428968,

        "numExtents" : 74,

        "indexes" : 22,

        "indexSize" : 653840,

        "fileSize" : 14608384,

        "nsSizeMB" : 16,

        "dataFileVersion" : {

                "major" : 4,

                "minor" : 5

        },

        "extentFreeList" : {

                "num" : 0,

                "totalSize" : 0

        },

        "ok" : 1

}

This is my file structure.

-rwxr-xr-x 1 mongodb mongodb          6 Oct 23 09:32 mongod.lock

-rw------- 1 mongodb mongodb   67108864 Oct 23 09:33 local.0

drwxr-xr-x 7 mongodb mongodb       4096 Dec 17 13:23 moveChunk

drwxr-xr-x 2 mongodb mongodb          6 Dec 24 09:24 _tmp

-rw------- 1 mongodb mongodb 2146435072 Dec 24 09:26 aureporting.8

-rw------- 1 mongodb mongodb 2146435072 Dec 24 09:26 aureporting.10

drwxr-xr-x 2 mongodb mongodb         40 Dec 24 17:12 journal

-rw------- 1 mongodb mongodb 2146435072 Dec 29 10:39 aureporting.7

-rw------- 1 mongodb mongodb  134217728 Dec 29 10:43 aureporting.1

-rw------- 1 mongodb mongodb   67108864 Dec 29 10:54 aureporting.0

-rw------- 1 mongodb mongodb   16777216 Dec 29 10:59 local.ns

-rw------- 1 mongodb mongodb   16777216 Dec 29 11:00 aureporting.ns

-rw------- 1 mongodb mongodb 2146435072 Dec 29 11:00 aureporting.9

-rw------- 1 mongodb mongodb  268435456 Dec 29 11:00 aureporting.2

-rw------- 1 mongodb mongodb  536870912 Dec 29 11:00 aureporting.3

-rw------- 1 mongodb mongodb 2146435072 Dec 29 11:00 aureporting.6

-rw------- 1 mongodb mongodb 2146435072 Dec 29 11:00 local.1

-rw------- 1 mongodb mongodb 2146435072 Dec 29 11:00 aureporting.5

-rw------- 1 mongodb mongodb 1073741824 Dec 29 11:00 aureporting.4

I would like to get some inputs from you guys to reduce some spaces from the system. At the moment it using 18GB of my storage. The application is sensitivity to the downtime but any help is greatly appreciated. 

This article is an interesting one. 

http://blog.mongolab.com/2014/01/managing-disk-space-in-mongodb/

Check out the part about resyncing nodes. It also has a link to this section of an article, which is probably the process you are looking for.

http://docs.mongolab.com/ops/#rolling-node-replacement