Backup and Temporary Files
Backing up your database
Depending on the configuration, Jease stores all data in a folder called "db4o" or "perst" (per default located in your home-directory). Simply backup this folder and you're done with your backup.
Jease creates a hot backup of your main database file (only the structure of the content tree, no binary content is included in this file) automatically every hour in your database folder. These files are tagged with the date of the backup. You should keep and backup some of them to be better safe than sorry, although I've never experienced a database corruption working with db4o or Perst for several years now. I would recommend to delete old files from time to time.
Please note: as Jease is built on an object-database, you'll need all classes which got stored in the database to reopen a database. So a general advice is to create a backup of your Jease-instance (usually jease/webapps/ROOT), too.
Temporary Files
Jease creates temporary files and directories in several locations depending on the overall configuration of your system (e.g. jease/temp and/or /tmp). This files are usually prefixed with jfix-*. It is recommended (and safe) to delete this files from time to time.
Please note: I would recommend to add a cleanup procedure to your start/stop-script and clean the directories when stopping your server.