Note: I’m attaching a video below demonstrating the issue. In it I’m reproducing the problem with the amd64 ISO of 15.04.

Steps to reproduce:
1. Have a (virtual) machine with a clean 10 GB hard disk and 8 GB of RAM.
2. Start the installer, select ”Erase disk and install Ubuntu”, click ”Install now”.

What happens:
A ”Do you want to return to the partitioner?” window pops up, saying ”Some of the partitions you created are too small. Please make the following partitions at least this large:

/ 3.5 GB

If you do not go back to the partitioner and increase the size of these partitions, the installation may fail.”

Selecting Continue then goes on to an installation which fails due to lack of space as promised. This is because the installer has partitioned the disk with a 8+ GB swap partition, and only what remains of the 10 GB after that allocated to /.

What I expect to happen:
I know this is a tricky corner case, but I think there are better ways to deal with it than exhibited by the installer above. Here are some alternative suggestions I came up with:

1) change the way the disk space requirement is calculated for the ”Preparing to install” view: make it require at least the minimum ”/” size + expected swap size, thus notifying the user beforehand if the requirement is not met. (As you see in the video, currently it has the green checkmark even when the installer is about to fail predictably.)

2) have the installer select a partitioning scheme where ”/” is the minimum required and allocate whatever remains for swap; warn the user that swap will be too small to do hibernation.

3) at the very least, have the ”Do you want to return to the partitioner?” window describe the situation better. It was the biggest source of confusion for me because the wording implied I had partitioned the disk (which I hadn’t done) and prompting me to ”return to the partitioner” where I hadn’t been to.