Excellent response, it's amazing how many people have never seen a SQL server with 200 disks attached to it, and we're not even talking about SANs. A single quad core chip can easily drive 200 disks. All people see is a $200,000 price tag for a single system and ignore the fact that it will outperform 100 $2000 servers. AMD64 can scale so far these days there is little point to NoSQL for all but the highest end of web-scale. I bet if you look into the core of Google there are still mysql systems doing a lot of grunt work.
Facebook still has MySQL doing a bunch of grunt work, but they're basically treating it like a NoSQL store - sharded key-value storage and that's it. They're moving to HBase now.
And, yeah, damn right I'm hesitant about a single piece of hardware that costs $200k and still leaves you with a SPOF. Effectively you're saying it's a 400k piece of hardware after replication. Oh, and Oracle replication software costs you an extra several hundred thousand. So for about a million dollars, yeah, unless it's incredibly transactional in nature, I'd give other options a very serious look.
It costs $5k for SQL Server with replication, you can use SQL Express for the monitor so all you're looking at is the 5K license you'd need for SQL Server Standard, if you need Enterprise it's only 20K. This are all retail prices which no one actually pays.
Ok, and if you have 50GB of data and have made a determination that SQL Server has some features that you're willing to pay 5k for, fine.
I still think embedding all your app logic together with your underlying data in PL/SQL or any equivalents is a bad idea but hey that's for anyone to do and find out themselves :)
