Instead, you attach a 2010 content database to the 2013 farm. You have the option of retaining the content database as a 2010 content database and to perform what is called a “deferred site collection upgrade.” In essence, this means that the 2010 site collection continues to be a 2010 site collection, just running on a 2013 farm. This is very different than the “visual upgrade” from 2007 to 2010. When you upgraded from 2007 to 2010, the site was upgraded, which meant you had to ensure compatibility. But a master page and other trickery made the site retain the appearance of a 2007 site. In 2013, that option no longer exists. Instead, the 2013 farm retains the 2010 “14 Hive”—with all of its features, site definitions, etc.
So, in theory, all of your 2010 sites will work perfectly well, customization included, in 2013. When you perform a deferred site collection upgrade, you are conceptually “flipping the switch” so that the site collection now runs against the “15 hive”. That is when compatibility might matter.
So, keeping this very high level, the theory is that you could upgrade your farm this weekend to 2013, and your users would be none the wiser. That’s certainly the type of platform upgrade path that Microsoft wants and needs in the cloud (Office 365).
We will see, shortly, just how well it works in the real world. But my guess is we will be much closer to a happy story than to an unhappy story. And, obviously, you will want to test the upgrade process before you actually perform it. But the bottom line is that we’re close to a point where upgrading the platform will become a non-issue, a very minor issue, or at least not a multi-month, insane project.
Because you are likely going to find that you can upgrade smoothly, you can move collaboration workloads from 2010 to 2013 quickly, or implement plans for 2010 in 2013 instead, as 2013 still supports 2010-style customization, workflows, etc.
You can learn more about upgrading to SharePoint 2013 in the Reference Link. As with all other upgrades, there’s no direct upgrade path from 2007 or earlier versions of SharePoint to 2013. You either have to go through 2010 on the way, or use a third party tool. And—knowing that you probably did things in 2007 that you would not choose to do the same way in 2013—I’d strongly recommend a good third party migration tool.
This should give you plenty to chew on for the next few days. Next week, we’ll look at some of the reasons people give me for not moving to SharePoint 2013, including the infamous “we always wait for Service Pack 1” argument. So this discussion is definitely not finished. See you next week!