The maximum size for a 4D data segment or a 4D Backup segment is 2 gigabytes. The one exception to this should be made to the first data segment because the first data segment not only stores data but also stores a path to the other data segments. Therefore, if a database is expected to exceed 2 gigabytes of data, it is recommended that the first segment should be defined to store no more than 1950 megabytes of data.
If by chance you have 2 gigabytes of data in the first data segment, and no other data segments have been defined, you will need to compact the data file. While compacting the data file, it will be possible to define more than 1 segment. The steps for adding segments while compacting are listed in the tech tip Changing 4D data segment sizes.
The reason for having the first data segment size smaller than 2 gigabytes only applies to the first segment. There are no other reasons, based on the needs of 4D, 4D Server, 4D Backup, 4D Tools etc.., that any other data or backup segment needs to be made smaller than the the 2 gigabyte limit.
For more information about segmenting a data file, check out Data Menu section of the 4D Server Reference Manual