title: MongoDB and disk space
body: <p>We have a MongoDB cluster with 4 shards.
  Our primary shard disk space has 700GB, and according to db.stats() that shard is using ~530GB.
  When checking df -h, the disk usage is on 99% (9.5 GB free), i'm guessing this means that all the rest is data files pre-allocated by Mongo.
  I've ran compact on couple of collections, and the disk space was reduced to 3.5GB(?)</p>
  
  <p>We're going to run a process that will generate ~140GB of extra data (35GB per shard).
  Should we have any concerned on running out of disk space?</p>
  
  <p>Thanks in advance.</p>