Redis is an open source key-value repository. It is a server that keeps data as strings, hash, list, set and ordered list, and allows to use various data structures. Redis is quite fast like Memcached, but it is different from Memcached.
Memcached can only input and output data. Redis supports many atomic functions because it uses data structures. With Redis, you can add new strings and values to a string. Memcached keeps the data in memory but does not write the data it holds in the file. Memcached terminates when the server it is running on is closed
So is Redis? In Redis, the data is stored in memory, but the data can be written in discrete (file) at desired intervals. By providing memory as well as data diskette, it provides a more consistent and continuous database. As Redis writes data to a file during certain periods, there is no data loss.