Field SQL Storage module overview
The Field SQL Storage module provides data management for the Field module. This module uses the Field API to generate dynamic data tables for entities and fields. While this is a required core module, it may be replaced by other contributed modules that implement The Field Storage API.
This module is an internal developer API and provides no user interface.
The Field SQL Storage module was introduced in Drupal 7.
Standard data storage for a field. It's recommended you use _field_sql_storage_tablename to get the name of this table.
Standard revision storage for a field. It is recommended to use _field_sql_storage_revision_tablename to get the name of this table.
You might find this information in
$field['storage']['details'];. The usage of this array is very strongly discouraged and is known not to work in certain cases, like inside