hi, i am new to redis. I want to use redis as only one database in my application, which has online trading.

1. Redis is good to online trading web application? Is it safe?
2. Redis is an in-memory database,but after i close redis server, computer, and later restart computer and redis server, the data is still available.
   why the data is still there? I mean it is in memory, and will be lost when the computer is shut off.
   3.Just only use redis as my web app's db is good enough?
3. I didn't find a orm-like plugin or ruby gem for redis, i think redis gem is not good enough to save, update, read, delete data in my app, do you have a recommend one for me?

Thank you, :)