How to load a .tar file on a container

Hi guys,
Sorry but I am new here and also in general programming. Need your help.
I have an existing database file dump.tar from a Redis DB. I just want to start a new Redis container and load data from that tar file.
I tried to do this:

tar cvf dump.tar /data
docker run -d -v /data --name redis-dumps redis echo "Redis data container"
docker run --rm --volumes-from redis-dumps -v /data:/backup busybox tar xvf /backup/dump.rdb
docker run --rm --volumes-from redis-dumps busybox ls -l  /data
total 0
root@ip-172-31-35-57:/data# docker exec -ti ca.redis.8 /bin/sh
# pwd
# ls
docker run -d -p 6379:6379 --volumes-from ca.redis-dumps --name ca.redis.8 dockerfile/redis
root@ip-172-31-35-57:/data# redis-cli   dbsize
(integer) 0

Even I am reading a lot, of course I still lack of the theory and I bet you are laughing now…but I don’t understand why I am not able to map the tar file into the new busybox container and start Redis using dump.tar.

Any help is appreciated!