/dev/... is mounted; will not make a filesystem here!

[DavHau]

Prerequisites

• I have updated to the latest version using nix run --refresh github:nix-community/nixos-anywhere
• I have reproduced the issue with the --debug flag
• I have searched existing issues to make sure this isn't a duplicate

Bug Description

When a previous nixos installation failed while copying store paths, and then nixos-anywhere is executed a second time, it crashes because it cannot unmount the disk:

### Uploading install SSH keys ###
### Gathering machine facts ###
### Formatting hard drive with disko ###
umount: /mnt: target is busy.
[...]
mke2fs 1.47.2 (1-Jan-2025)
/dev/disk/by-partlabel/154842f3f4b6a1a55afdc3809550d04a7e8c is mounted; will not make a filesystem here!
+ rm -rf /tmp/tmp.hu1g7ygsjL

Steps to Reproduce

Debug Logs

.

Command Used

.

Target System

Cloud server (AWS, DigitalOcean, etc.)

NixOS Version

No response

Environment Information

• Host OS:
• Nix version:
• Target architecture:

Configuration Files

Additional Context

No response