Does your mosaic dataset have a lot of images (ten or hundreds of thousands)?
Are you using a 10.0 file geodatabase to manage your mosaic dataset?
Do you make frequent and massive data transactions and manipulations?
If you answered “yes” to all these questions, then there is a chance that the size of your file geodatabase on disk has increased exponentially and has become quite inflated. This is due to a common problem of any database system – fragmentation.
No need to panic
The solution to this problem is to run the Compact geoprocessing tool periodically on your file geodatabase. This tool will rearrange how the geodatabase is stored on disk, and will usually reduce its size, and improve its performance.
How about in 10.1?
In ArcGIS 10.1, this inflation is far less noticeable, because mosaic dataset uses the out-of-line storage. This means that any mosaic dataset that is within a file geodatabase created in 10.1 will not have a large inflation due to constant data transactions. Therefore you should consider migrating your mosaic dataset to a 10.1 created file geodatabase. Simply create a file geodatabase in ArcGIS 10.1, then copy and paste your mosaic dataset into it.
Is Compact obsolete in 10.1?
It is still a good practice to run the Compact tool occasionally in ArcGIS 10.1. It will only make a small difference after massive data manipulation, but it will still keep your file geodatabase organized neatly and running optimally.
Contributed by: Hua Wei