=====Overview=====
Xtrabackup (innobackupex) is a 3rd Party tool, developed by Percona and is able to provide with online backup for InnoDB and warm backup for MyISAM Tables.
The backup of the InnoDB is achieved using: innobackupex tool which is a symlink to the: Xtrabackup, as follows:

=====Backup=====
The backup seems pretty simple, just specifying the username, password and the backup destination:

<sxh bash>
[root@mysqlmaster ~]# innobackupex --user=root --password=<password> /backup/
180220 09:24:51 innobackupex: Starting the backup operation

IMPORTANT: Please check that the backup run completes successfully.
           At the end of a successful backup run innobackupex
           prints "completed OK!".
xtrabackup: Transaction log of lsn (2628243) to (2628252) was copied.
180220 09:25:25 completed OK!
[root@mysqlmaster ~]#
</sxh>


All the backup information including the log position and log name are recorded in the xtrabackup_info file:


<sxh bash>
[root@mysqlmaster ~]# cat /mysqldata/backup/2018-02-20_09-24-51/xtrabackup_info
uuid = e4183967-1649-11e8-bdce-08002795cbb8
name =
tool_name = innobackupex
tool_command = --user=root --password=... /mysqldata/backup/
tool_version = 2.4.9
ibbackup_version = 2.4.9
server_version = 5.7.21-log
start_time = 2018-02-20 09:24:51
end_time = 2018-02-20 09:25:25
lock_time = 0
binlog_pos = filename 'mysql-bin.000011', position '424'
innodb_from_lsn = 0
innodb_to_lsn = 2628243
partial = N
incremental = N
format = file
compact = N
compressed = N
encrypted = N
[root@mysqlmaster ~]#
</sxh>

Bear in mind that the locking is done ONLY for the MyISAM and non-InnoDB tables. InnoDB tables aren't locked and Percona will apply the redo logs to make the backup consistent as follows:

=====Prepare backup=====
In order for the backup to become consistent, we have to apply the logs on it. 

<sxh bash>
[root@mysqlmaster backup]#  innobackupex --apply-log /backup/2018-06-08_14-27-54/
180608 14:31:23 innobackupex: Starting the apply-log operation

IMPORTANT: Please check that the apply-log run completes successfully.
           At the end of a successful apply-log run innobackupex
           prints "completed OK!".

innobackupex version 2.4.9 based on MySQL server 5.7.13 Linux (x86_64) (revision id: a467167cdd4)
xtrabackup: cd to /mysqldata/backup/2018-06-08_14-27-54/
xtrabackup: This target seems to be not prepared yet.
InnoDB: Number of pools: 1
xtrabackup: xtrabackup_logfile detected: size=8388608, start_lsn=(2790154)
xtrabackup: using the following InnoDB configuration for recovery:
xtrabackup:   innodb_data_home_dir = .
xtrabackup:   innodb_data_file_path = ibdata1:12M:autoextend
xtrabackup:   innodb_log_group_home_dir = .
xtrabackup:   innodb_log_files_in_group = 1
xtrabackup:   innodb_log_file_size = 8388608
xtrabackup: using the following InnoDB configuration for recovery:
xtrabackup:   innodb_data_home_dir = .
InnoDB: page_cleaner: 1000ms intended loop took 6991ms. The settings might not be optimal. (flushed=0 and evicted=0, during the time.)
InnoDB: FTS optimize thread exiting.
InnoDB: Starting shutdown...
InnoDB: Shutdown completed; log sequence number 2790440
180608 14:31:35 completed OK!
[root@mysqlmaster backup]#
</sxh>