tldr: how do I erase all of the information from my startup disk? Logging into recovery mode and selecting "erase" has no affect on my disk's "free" space.
While attempting to diagnose an issue I was experiencing, I decided to erase my iMac's startup disk and then restore from a time machine backup. So I log into recovery mode, open up disk utility, and select "erase". Somewhat surprisingly, I see that, while the disk's "used" space drops to almost zero, all of the data seems to be transferred to the "other volumes" category, and the amount of "free" space on the disk doesn't change.
I assumed that this was simply a labeling issue, and that the operating system had earmarked all of this "other volumes" information to be deleted asap. So I opened up time machine and restored from backup. After having completed the time machine restore, I logged into find that all of that "other volumes" data was still taking up hundreds of gigabytes of space, and I had only ~20GB free on the computer.
So I try logging into recovery mode again and selecting "erase." This time it does free up all the "used" space, but it still leaves ~500GB of "other volumes" data.
So how do I actually erase all of the information on my startup disk? Logging into recovery mode and selecting "erase" seems to have no affect. Thanks!!