why the number of .frm files backuped is not enough

I’m a newer to the xtrabackup. The version of the xtrabackup installed is v1.5.1.
There are 100 .frm files in mysql data directory. However, there are only 8 .frm files in the backup data directory. I use the full backup command, such as
/usr/bin/innobackupex --user=$User --password=$Passwd --defaults-file=/etc/my.cnf --database=$Database $databak_dir

I view the backup log. No error hints occur.
121224 03:01:44 innobackupex: completed OK!
DataBase Backup Success

I wonder whether the backup is OK for xtrabackup?

I see in that command line that you are only backing up one single database. You should compare the number of tables on that database with the number of .frm files on the backup directory.

The log of the backup process will also help, attach it please.

I have sovled the problem. the problem is not due to innobackupex. Thanks!