WARNING !

The embedded database used in EMAN2 (which stores most of your image data and information about your projects in a set of EMAN2DB directories) has a number of very important limitations and restrictions associated with it. Failure to be aware of these restrictions could result in data loss and waste of your valuable time. Those of you accustomed to working with normal image files and moving them around manually need to be aware that you cannot do this with a database system as EMAN2 uses.

Brief technical explanation

Details on the database are discussed in Eman2DataStorage

EMAN2 uses an embedded database to store information about a project, as well as much of the actual image data. This choice was made for a number of reasons including performance, flexibility, and dealing with projects with thousands of micrographs and hundreds of thousands of particles. However, it comes with a few limitations. Like most databases, it uses a memory & disk cache to give faster access to information and coordinate access to the data from multiple programs (on the same machine). This cache consists of a set of files stored in /tmp (which must be physically attached to the local machine). If you try to access the same database from two different machines at the same time via a shared network filesystem, each machine establishes an independent cache in /tmp, and both think they have exclusive access to the files. This produces a situation where the machines can easily disagree about the contents of a file, and can cause database corruption. The 'e2bdb.py -c' program will safely close the cache on one machine, so it can be reliably accessed from another machine. It is also possible in some cases to open the databases read-only from multiple machines at once, with no cache, however this is a special case used in some situations on clusters, and not a general rule.

The files in the EMAN2DB directories are not normal flat image files, but are actually proprietary database files. Moving them around or otherwise messing with them will confuse the database. Just like you wouldn't create a MySQL database and go moving around its database files wily-nily, you shouldn't mess with files in the EMAN2DB directory, particularly if there is an active cache.