I am in the design phase of a new project and am trying to determine if MySQL Cluster is a viable option for the project I'm working on. It's a social network with many of the typical social network site features (profiles, photos, comments, videos, etc). We are using LAMP environment. I'm trying to research MySQL Cluster, MySQL Replication, and how other large sites cope with large amounts of traffic and how they solve their scalability and HA issues.

It seems everyone is recommending replication, but I have concerns about it:

1. Initially, we expect that there will be as many writes as reads as more and more users create profiles, post photos, comments, etc. Considering that replication is great for read-intensive applications, would replication be of any help here? How would I aleviate the large number of writes to a single master server?

3. Even if I partition my data across different master databases, if one of them fails then part of the site (and potentially the entire site) might go offline. Or am I wrong? Any thoughts on this scenario would be greatly appreciated.