I'm curious what the licensing costs are for their Microsoft stack. Stack Exchange was in BizSpark early on so they got a pretty good discount, but they can't be anymore since it's been more than 3 years.
With that said, we're getting amazing performance out of SQL Server without having to shard, etc: all of Stack Overflow runs off a single server, and most of the rest of Stack Exchange runs off a second server.
Three Dell R720xd database servers (two in New York City, one in Oregon, using SQL AlwaysOn Clustering) (Global "Sites" DB & Stack Overflow dedicated):
- 2x Intel Xeon Processor E5-2680 @ 2.70 GHz
- 384 GB RAM
- 21 drives
- Mirrored Pair for OS
- 16+1 Intel 710 200GB SSD RAID10 for databases
- SQL Server 2014 CTP2
- 2x 10Gb network teamA few services hit the read replicas instead of the primary (our API, for example, moves what it can when it can), but the code for stackoverflow.com is almost entirely querying a single (quite beefy) box.
We can and do sometimes run without either replica in the AG, though we prefer not to except for scheduled maintenance.