Are there some suggestions with SSD drives? Putting the DB into RAM and backing up periodically to disk is a valid solutions?
I have some very busy databases on SSD-only systems. I think you're using SSDs that are not rated for server use.
Your strategy of using in-ram disk and backing up to the SSD is sensible, depending on what guarantees you need for the data to survive an unclean system shutdown. You will want to use a file system that allows you to snapshot and backup or logical DB backups. Postgres 9.4 has some features that will make taking the backup from the file system much easier and cleaner, too.