The innodb_data_home_dir default value is the MySQL data directory (datadir).
innodb_data_home_dir ：The common part of the directory path for InnoDB system tablespace data files.
innodb_data_file_path ：Defines the path and file size for individual InnoDB system tablespace data files. The full directory path for system tablespace data files is formed by concatenating path defined by innodb_data_home_dir and innodb_data_file_path. If you specify the value as an empty string, you can specify an absolute file paths for innodb_data_file_path.
datadir：
The path to the MySQL data directory
eg：
[mysqld]
innodb_data_home_dir =
innodb_data_file_path=/path/to/myibdata/ibdata1:50M;/path/to/myibdata/ibdata2:50M:autoextend