I wanted to upgrade my Fedora Core 6 to Fedora 7. I was shocked to find out that
Fedora no longer has CD ISOs, and since I do not have a DVD writer, I had no
choice but to put the DVD ISO on my hard disk, boot from a rescue disk, and
choose tell it to upgrade using an ISO on my disk.

I had no problems to boot the CD, choose installation from HD, and tell it where
the ISO resides. The installer recognized that this was a valid ISO, and continued.

But then, a "Looking for existing installations" message popped up, and a few
seconds later, an installation screen came up asking me to reformat my
partitions. I was NOT asked whether I want a new installation or an upgrade, so
evidently the existing installation wasn't recognized.

After a lot of retries (which all failed in the same way) and a lot of
soul-searching, I figured out the probably cause for the bug: The ISO I was
installing from was on the same partition I was hoping to upgrade - my only
partition. It is possible that the installer first mounted the partition to read
the ISO, and then wanted to mount it again for looking for an installed system,
and the second mount didn't work. So I put a second disk in my system, put the
ISO there, and sure enough: now the "looking for existing installations"
succeeded, and I was asked whether I want to upgrade, or do a fresh install.

I think it is extremely important that you fix this bug. A significant number of
PCs still don't have a DVD writer, and have just one disk, and since the
"install from hard disk" is the method you suggest in your documentation, all of
these people are likely to run into this same bug!

I also urge you to reconsider your decision not to provide CD ISOs, even if only
by bittorrent. Of course, this is irrelevant to the current bug report.