When performing a local backup, multiple files can be copied concurrently by using the --parallel option. This option specifies the number of threads created by xtrabackup to copy data files.
To take advantage of this option whether the multiple tablespaces option must be enabled (innodb_file_per_table) or the shared tablespace must be stored in multiple ibdata files with the innodb_data_file_path option. Having multiple files for the database (or splitting one into many) doesn’t have a measurable impact on performance.
As this feature is implemented at a file level, concurrent file transfer can sometimes increase I/O throughput when doing a backup on highly fragmented data files, due to the overlap of a greater number of random read requests. You should consider tuning the filesystem also to obtain the maximum performance (e.g. checking fragmentation).
If the data is stored on a single file, this option will have no effect.
To use this feature, simply add the option to a local backup, for example:
$ innobackupex --parallel /path/to/backup