I applied through employee referral.

First round: Skype interview. Just a couple of coding questions on hash tables, networking, Linux commands, and SQL.

Next, they called me for F2F.

First round: Coding on a whiteboard. Designing questions, hash tables, puzzles, DS, and Algorithms.

Second round: System designing, OS in depth, DBMS queries, and Networking in depth.

Manager round: Normal questions like how CDN works, why you left your previous company, etc..

HR round: About my role, my experience, and salary.

Just go through "Cracking the Coding Interview". This is fine for almost every interview.

Design a file system.