xtrabackup not recover my table

i try xtrabackup --backup --datadir=/var/lib/mysql/ --target-dir=/root/backup/
xtrabackup --prepare --target-dir=/root/backup

and then drop table a;
rsync -avrP /root/backup/ /var/lib/mysql/
chown -R mysql:mysql /var/lib/mysql,

but when i relogin mysql,and check database test1 the table a not exist!
the table a is innodb engine,why not recover?

i see mysql test1 database directory contains a.frm a.ibd ,but after rsync,this a table not restore