Volatile management

The /volatile area is managed by a software system that cleans up
the area periodically in multiple steps listed below. The first two
steps will always take place. The third and forth steps will been proceed if the total usage
for all projects of the volatile area is still not below the target.

1. All files that have not been used for more than 6 months will be deleted.
2. If a project exceeds its quota and the Lustre file system reaches its deletion threshold, the least-recently-used (LRU)
   files will be deleted until the total usage of the project is below its
   quota.
3. Each file is assigned a deletion index that combines the excess
   usage of a project over its reservation coupled with the period of time
   the file is modifed. The clean up process will delete files
   according to the index in a descending order until the total /volatile
   usage is below the managed area's target and Lustre space is under its deletion threshold.
4. When Lustre total usage is reached to a critical point, additional file deletion will be performed (using file deletion index).