ibdata is the usual prefix name of InnoDB's System Tablespace.
The default system tablespace name is ibdata1.
Please note InnoDB Architecture
From the above diagram, ibdata1 can contain the following:
- Data Dictionary
- Double Write Buffer (used in Crash Recovery)
- Insert Buffer (Used to update Secondary Index change from Buffer Pool)
- Rollback Segments
- Undo Space
- Data Pages from InnoDB Tables (innodb_file_per_table disabled)
- Index Pages from InnoDB Tables (innodb_file_per_table disabled)
Adding additional ibdata files results in spreading these seven(7) classes of InnoDB info