How can MongoDB dataSize be larger than storageSize?

Question

As far as I understand, the storage size for MongoDB should always be larger than data size. However, after upgrading to Mongo 3.0 and using WiredTiger, I start seeing that

Answer 1

MongoDB 3.0 with WiredTiger engine uses 'snappy' compression by default. If this affects your DB performance, you can consider to turn it off (blockCompressor: none) in the mongod.conf file:

storage:
  engine: wiredTiger
  wiredTiger:
    collectionConfig:
      blockCompressor: none