SQL Server equivalent to functionality of Oracle RAC? I did some Googling and couldn't find an answer to this question more recent than a few years ago, so I thought I'd ask. Oracle's RAC feature offers load-balancing for both read and write transactions, as well as scale-out and high-availability without downtime (at least, as I understand it - we're about to deploy our first databases that use RAC, so we'll see how it goes).

Is there any SQL Server feature set (or third party component you could install on top) that delivers equivalent functionality? We've always used Windows clustering, where a failover event causes about 20-30 seconds of SQL downtime - always tolerable, but not ideal. Now, with AlwaysOn in SQL 2012, SQL Server shrinks that to about 15 seconds and adds the concept of read-only-secondary databases, but they still require that write transactions are choked through a single connection point (much improved, since many transactions are just read, but still not really load balancing), and in the case of a node failure or the need to patch, there's still downtime.

I suppose it's just more curiosity - I feel like this is the only area that SQL Server falls behind Oracle (at least among the features I've personally seen used). I wanted to see if there are any options out there to close that gap and possibly improve our own SQL Server deployment while we wait for Microsoft's equivalent feature to be added - maybe in SQL 2014/2015?
No, nothing in SQL Server can give you the same thing out of the box.

Currently, the only SQL Server technology that allows simultaneous writes at multiple nodes is Peer-to-Peer replication. Note that I did not to say "write scale-out," because it works in a way such that the entire system has the write capacity of only a single node. The introductory paragraph of that page is worded carefully to include the term "scale-out" without saying "write scale-out." Yay for marketing-speak.

From what I've read, Oracle RAC is the same in that respect. Functionally, the only thing that's missing from SQL Server in this configuration is a load-balancing solution, which is both an advantage (you can implement it any way you want) and a disadvantage (it's not in the box or supported by Microsoft) when comparing against competing products.

Conversely, Oracle RAC does not give you the same thing as SQL Server out of the box either. For example, RAC is recommended to be implemented with nodes within 100km of each other because of realtime network latency, whereas Peer-to-Peer replication has no such restriction. (I'm not saying one solution is better than the other: I'm just pointing out that they are different. The business should choose a solution that best fits their specific needs.)