[nickpsecurity]

Here's the only page I could quickly find on Github's architecture for those interested:

https://github.com/blog/530-how-we-made-github-fast

This looks like a single datacenter. I don't see anything here indicating high availability or other datacenters. You'll usually spot either an outright mention of it or certain components/setups common in it. They might have updated their stuff for redundancy since then. However, if it's same architecture, then the reason for the downtime might be intentional design where only a single datacenter has to go down.

Might be fine given how people apparently use the service. It's just good to know that this is the case so users can factor that into how they use the product and have a way of working around the expected downtime if it's critical to do so.