Difference between Retract solution and Remove solution in SharePoint

Question

In Central Administration if I go to "System Settings > Manage farm solutions" I can see my deployed solutions (via Visual Studio). Clicking on any of my deployed solution takes me to "Solution Properties" which shows option of Retract Solution. Once I have retracted my solution I am presented with another option of Remove Solution. Removing the solution removes the entry from "Manage farm solutions".

I would like to know:

1. What is the difference between Retract Solution and Remove Solution?
2. Why are two options provided by Microsoft?
3. I noticed that after retracting solution my solution folder in TEMPLATE\CONTROLTEMPLATES was empty but it was still there, but my solution folder in TEMPLATE\LAYOUTS was removed completely. Any reason for this behaviour?

Answer 1

1. Retract Solution fires off the Uninstall process of the WSP package from the farm. It's equivalent to the Uninstall-SPSolution PowerShell command and the opposite of the Install-SPSolution command.

   Remove Solution is the equivalent of the Remove-SPSolution PowerShell command and is the opposite of the Add-SPSolution command. It can be seen as deleting the file from the system (The WSP is removed from the Configuration Database).

2. They are different things, with the first, SharePoint still has the instructions/artifcats for installing/removing the features included in the package, with the second, SharePoint forgets it ever existed.

3. After a retract, the files are only stored inside the WSP that's stored in the configuration database. The Install/Deploy commands are responsible for unpacking the WSP and applying the instructions declared inside it, including file system modifications.

   If SharePoint didn't delete a folder/file it might have been in use when it reached that removal step or something made it think it shouldn't delete the file. The actual reason for that is hard to say.