Unable to take backup of mysql database using Xtrabackup

Question

I am trying to take mysql backup without any downtime but unable to take the backup using Xtrabackup .

Actual Database is almost about 40+ GB in size. I am trying to first satisfy myself. Hence, I have created a sample database on a server with 5000 Tables (all InnoDB tables). As per the blog "there are some cases when you can get table entirely missing from the backup if you use this technique " "--single-transaction are not safe to use on production environment.

[root@localhost mysql]# mysql
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 56
Server version: 5.5.25a-log MySQL Community Server (GPL) by Remi
mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| innodbtest         |
| mysql              |
+--------------------+
3 rows in set (0.00 sec)
mysql> use innodbtest;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Database changed
mysql> show create table T4000;
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                      |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| T4000 | CREATE TABLE `T4000` (
  `A` int(11) NOT NULL,
  `B` int(11) DEFAULT NULL,
  `C` char(1) DEFAULT NULL,
  PRIMARY KEY (`A`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> show create table T3040;
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                      |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| T3040 | CREATE TABLE `T3040` (
  `A` int(11) NOT NULL,
  `B` int(11) DEFAULT NULL,
  `C` char(1) DEFAULT NULL,
  PRIMARY KEY (`A`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql>

I used tool xtrabackup and followed the steps to create a backup

xtrabackup --backup --datadir=/var/lib/mysql --target-dir=/opt/bkp/

After taking the backup I am not getting the ".ibd" files at the backup location.

[root@localhost mysql]# ls -al /opt/bkp/
total 190676
drwxr-xr-x 2 root root      4096 Nov 27 19:02 .
drwxr-xr-x 5 root root      4096 Nov 27 18:08 ..
-rw-r----- 1 root root 195035136 Nov 27 19:02 ibdata1
-rw-r----- 1 root root        79 Nov 27 19:02 xtrabackup_checkpoints
-rw-r----- 1 root root      2560 Nov 27 19:02 xtrabackup_logfile
[root@localhost mysql]#

After restoring the database using xtrabackup, I am not getting the database folder "innodbtest" on the other server too.

Where am I wrong?