I was running Ubuntu Server on a mdadm RAID1 volume, and I ran into some problems so I decided to just do a clean install.
I booted with Gparted, stopped the mdadm array, and ran
--zero-superblockon each partition, then deleted the partitions using Gparted.
I then booted from an Ubuntu Server USB, configured the raid from scratch using the manual partitioning option, and installed Ubuntu 18.04.
First thing after installing the OS, I installed xfce4 and firefox along with a few other standard utilities and rebooted ran startx and fired up Firefox.
When logged I logged in, the tabs that I had open before reinstallation immediately opened up, I was still logged into SO. In fact, my entire home folder was still there.
I thought I had nuked everything and started fresh. I am totally mystified as to how this happened. Upon further inspection, I saw that all my files in my home folder were still there as well.
Is there some step that I missed? I thought the point of --zero-superblock and deleting the partitions was to get rid of any data on the drive. What did I miss? What does it take to do a guaranteed truly clean install? I am certain I have followed the same exact procedure before and my home directory did not persist.
Edit: So I zeroed out the component drives of the array, but now in the manual setup in the installer, I cannot set my new partition to "bootable" (nothing changes when I select it). Oddly, when creating the partitions it no longer asks me if I want to do a primary or a logical partition as it has in past times USING this same installer usb.