What is GridFS?

What is it ?
a way to store files in your database that doesn's suck.
a way to ensure that metadata is always kept with a file.
a way to get all the scaliing benefits of mongodb for files.
How Does it work?
Splits large object into small chunks 16mb in size . Each chunk is stored as a separate document in a chunks collection. Metadata about the file,including the filename, content type, and any optional information needed by the developer, is stored as a document in a files collection. These collections can have an abritrary namespace!
The size of each chunk. GridFS divides the document into chunks of the size specified here. The default size is 255 kilobytes. Changed in version 2.4.10: The default chunk size changed from 256k to 255k.
When querying, eache chunk is found and streamed seperatly keeping the amount of data in the buffer low GridFS places the collections in a common bucket by prefixing each with the bucket name. By default, GridFS uses two collections with names prefixed by fs bucket:
fs.files
fs.chunks

Chunks
{
  "_id" :,  // object id of the chunk in the chunks collection
  "files_id" :,  // id of the corresponding files collection entry
  "n" :,  // chunks are numbered in order, starting with 0
  "data" :  //the chunk's pay load as a BSON binary type
}
Files
{
id,  // objectid
filename, // the file name
chunksize, // the size of eache chunk
upladdate, // the date the record was creaed.
md5,  // md5 hash of the complete file
length  // todal length of the file bytes
}

Why should i use it?

Archiving
Highly avaliable
Meatadata
Versioning
Dynamically expand capacity

Take a example.

[mongo@db231 ~]$ touch a.txt
[mongo@db231 ~]$ mongofiles put a.txt -u anbob -p mongo
connected to: 127.0.0.1
added file: { _id: ObjectId('5366f3f917d265ad5f30fde6'), filename: "a.txt", chunkSize: 261120, uploadDate: new Date(1399256057438), md5: "d41d8cd98f00b204e9800998ecf8427e", length: 0 }
done!
[mongo@db231 ~]$ mongofiles list -u anbob -p mongo
connected to: 127.0.0.1
a.txt   0
[mongo@db231 ~]$ mongofiles get a.txt -u anbob -p mongo
connected to: 127.0.0.1
done write to: a.txt
[mongo@db231 ~]$ mongofiles put b.txt -u anbob -p mongo 
connected to: 127.0.0.1
added file: { _id: ObjectId('5366f4929f9a51b6a19d1de0'), filename: "b.txt", chunkSize: 261120, uploadDate: new Date(1399256210648), md5: "d41d8cd98f00b204e9800998ecf8427e", length: 0 }
done!
[mongo@db231 ~]$ mongofiles list -u anbob -p mongo     
connected to: 127.0.0.1
a.txt   0
b.txt   0
c.txt   12640
[mongo@db231 ~]$ mongofiles search a -u anbob -p mongo    
connected to: 127.0.0.1
a.txt   0
[mongo@db231 ~]$ mongo -u anbob -p mongo               
MongoDB shell version: 2.6.0
connecting to: test
> show databases;
admin  0.078GB
local  0.078GB
test   0.078GB
> use test
switched to db test
> show collections;
fs.chunks
fs.files
impuser
system.indexes
testtab
> db.fs.files.find();
{ "_id" : ObjectId("5366f3f917d265ad5f30fde6"), "filename" : "a.txt", "chunkSize" : 261120, "uploadDate" : ISODate("2014-05-05T02:14:17.438Z"), "md5" : "d41d8cd98f00b204e9800998ecf8427e", "length" : 0 }
{ "_id" : ObjectId("5366f4929f9a51b6a19d1de0"), "filename" : "b.txt", "chunkSize" : 261120, "uploadDate" : ISODate("2014-05-05T02:16:50.648Z"), "md5" : "d41d8cd98f00b204e9800998ecf8427e", "length" : 0 }
{ "_id" : ObjectId("5366f4b9b4651853819dff35"), "filename" : "c.txt", "chunkSize" : 261120, "uploadDate" : ISODate("2014-05-05T02:17:29.648Z"), "md5" : "3614afb5016f2495811bd500e6719285", "length" : 12640 }
> db.fs.chunks.find();
{ "_id" : ObjectId("5366f3f991d72e59b571490a"), "files_id" : ObjectId("5366f3f917d265ad5f30fde6"), "n" : 0, "data" : BinData(0,"") }
{ "_id" : ObjectId("5366f49291d72e59b5714913"), "files_id" : ObjectId("5366f4929f9a51b6a19d1de0"), "n" : 0, "data" : BinData(0,"") }
{ "_id" : ObjectId("5366f4b991d72e59b5714918"), "files_id" : ObjectId("5366f4b9b4651853819dff35"), "n" : 0, "data" : BinData(0,"VUlEICAgICAgICBQSUQgIFBQSUQgIEMgU1RJTUUgVFRZICAgICAgICAgIFRJTUUgQ01ECnJvb3QgICAgICAgICAxICAgICAwICAwIEFwcjMwID8gICAgICAgIDAwOjAwOjAyIGluaXQgWzVdICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAKcm9vdCAgICAgICAgIDIgICAgIDAgIDAgQXByMzAgPyAgICAgICAgMDA6MDA6MDAgW2t0aHJlYWRkXQpyb290
...
-- over