Redis persistence is described in detail here:

http://redis.io/topics/persistence

By default, redis performs snapshotting:

By default Redis saves snapshots of the dataset on disk, in a binary file called dump.rdb. You can configure Redis to have it save the dataset every N seconds if there are at least M changes in the dataset, or you can manually call the SAVE or BGSAVE commands.
For example, this configuration will make Redis automatically dump the dataset to disk every 60 seconds if at least 1000 keys changed: save 60 1000

Another good reference is this link to the author’s blog where he tries to explain how redis persistance works:

http://antirez.com/post/redis-persistence-demystified.html