I have some knowledge about file Geodatabase.

File geodabase is the personal Geodatabase storage format developed by ESRI Despite Microsoft Access capacity restrictions.

1. Advantages of file Geodatabase:

1) cross-platform support for Windows, Linux, and Solaris

2) fgdb supports all Geodatabase features, including vector, raster, Terrian, and annotation.

3) Massive Data support: each data set supports 1 TB of data. In principle, it depends on the size of the storage space (this advantage is indeed good and useful in data backup and recovery ).

4) file geodabase supports data compression

5) it can represent the spatial relationship between data and make queries fast (this is not found yet)

II. in development, the interface involved in file geodatabase is filegdbworkspacefactory. This interface is used to create and open file geodabase. the methods for creating feature dataset, feature class, and table in file geodabase are the same as those for creating feature dataset, feature class, and table in SDE, because they are inherited from the workspace factory interface, for details, refer to the OMD diagram.

Iii. Comparison of Three geodatabases

(Translated from the ESRI official forum. If the translation is inaccurate, please forgive me !)

	ArcSDE Geodatabase	File Geodatabase	Personal Geodatabase
Description	Store different types of GIS data in relational databases as tables.	Place different types of GIS datasets in a folder. We recommend that you use file Geodatabase to store and manage local files.	Before data is stored in ArcSDE Geodatabase, it is generally stored in access for ease of management, This method is limited by the storage space (up to 2 GB) and the Operating System (only on Windows)
Number of users	Multiple users ArcSDE includes three types: 1. Personal ArcSDE 2. workgroup ArcSDE 3. Enterprise ArcSDE	Single user and group use Each dataset can have several read permissions, but only one write permission.	Single user and group use Each dataset can have several read permissions, but only one write permission.
Storage Method	Large databases such as Oracle, Microsoft SQL Server, IBM DB2, and IBM Informix	Each dataset is an independent file. A file database is a file containing many data files.	Stored in Microsoft's Access Database (. mdb Format)
Space limit	Depends on the storage space of the database	One dataset can store 1 TB of data. Each file database can contain many datasets.	The maximum storage space is 2 GB, but in order to maintain a high level of database efficiency, the space should be limited to MB.
Supported versions	All databases are supported, including cross-database updates and changes	Not Supported	Not Supported
Platform	Windows, UNIX, Linux, etc. You can connect to a database on any platform in the LAN by directly connecting to the database.	Cross-platform	For Windows operating systems only
Security and reliability	Security mechanisms implemented by Databases	Operating System-dependent security lines	Windows File System Security
Database Management Methods	Space Data is managed by tools provided by the database	File System Management	Windows File Management
Notes	Must be used with ArcSDE	When the storage space is too large, you can adopt the read-only compression mode to reduce the space