redis persists its memory data in snapshot style in every n seconds depending on your configuration.
read more here.
perhaps you would like to use redis as a pure in-memory db, like f.e. memchache.
you can tell redis to not persist and save some bits&miliseconds.
this could be the case when using redis as a f.e. realtime queue, you wont need persistence,
because you could say: nobody needs is newsfeed from the that day before the machine crashed ;)
alright, do so by:
you will find:
# Note: you can disable saving at all commenting all the "save" lines. save 900 1 save 300 10 save 60 10000
do as you are told:
#save 900 1 #save 300 10 #save 60 10000
then restart redis.
sudo /etc/init.d/redis-server restart