Upgrade is always painful. SharePoint is no exception. Microsoft has suggested two ways of upgrade: inplace and database upgrade. All articles suggest database upgrade, which is also my choice. I don't trust third party migration tools. They will mess up the whole thing as I tried the most famous one, and missed a lot of things. However I don't trust Microsoft either, maybe SharePoint itself too.
Firstly I exported content database to new farm. The PowerShell window in SharePoint 2010 menu must be opened as Administrator. Run Test-SPContentDatabase in the new farm then it reported some error. Check the log it says some features are missing. Those features have already deleted but some elements still reference to them. After some search I found a tool that claims to remove even the toughest features. It's called WssRemoveFeatureFromSite written by an MS guy. Still one feature can't be deleted. My colleage suggested me to create a dummy feature using the same GUID. It's brilliant and did work! Deploy the feature, and delete it using the tool or even stsadm command in the original farm. Export the content database again, and run Test-SPContentDatabase. This time only warnings, no errors.
I thought it will be a smooth upgrade experience from then on. I was wrong. Tried many times of Dismount-SPContentDatabase and Mount-SPContentDatabase still it reported as if the whole database was broken. I tried back and forth, nothing indicate the problem. No error log, no clue at all. Frustrated, and seeked help online. Nobody had the problem. In the end, I have no way but follow the official guidance to redo in database backup/restore approach. This time it seemed work, eventually. But why???
Anyway it worked. After this step it's time to deploy all custom features, solutions etc to the site. Because the cab file structure is the same, not much is required to change in the solution files. Just remember to change the reference to the new Microsoft.SharePoint and similar assemblies. Build the solution files again, and here you go!
The new site will look exactly like the one before, include site admin and all other UI. Boss won't happy because there's no ribbon, just like the previous version. Ok. Let's delete the content database and redo the content database upgrdade. This time with -UpdateUserExperience switch.
Now the whole site will use the v4 master page. You can go to SharePoint designer 2010 and choose your own master page, apply it recursively. Wait, you still can't see the ribbons etc because you didn't include them in your master page. Follow this MSDN article to add ribbons on your old master page: http://msdn.microsoft.com/en-us/library/ee539981%28office.14%29.aspx
For me I also extended <div id="s4-workspace"> to <div id="s4-workspace" class="s4-nosetwidth"> because the right edit panel will out of screen in Web Part edit mode.
Now at least it seemed right.
