Can't install alongside existing Arch installation

Help
1

I would like to give NixOS a try, but when I try to run the first command of the 2.2.2. Legacy Boot (MBR) section, I get the following error:

Warning: The existing disk label on /dev/nvme0n1p3 will be destroyed and all
data on this disk will be lost. Do you want to continue?
Yes/No?                                                                   
Yes/No? Yes                                                               
Error: Partition(s) 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,
18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36,
37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55,
56, 57, 58, 59, 60, 61, 62, 63, 64 on /dev/nvme0n1p3 have been written, but we
have been unable to inform the kernel of the change, probably because it/they
are in use.  As a result, the old partition(s) will remain in use.  You should
reboot now before making further changes.

The command is parted /dev/nvme0n1p3 -- mklabel msdos

Here is my current disk layout:

image
image1922×1050 101 KB

I would like to install it in the /dev/nvme0n1p3 partition.

Any help is appreciated.

2

You have an esp, why do you want to install legacy boot cruft into the MBR a partition? Even if the disk is not GPT, a partition doesn’t have an MBR… It’s per disk.

Just use EFI. Perhaps a second ESP, to make sure nothing clashes.

3

You’re trying to create a partition table on a partition instead of a device - that’s why you get the weird error.

Just create the file system instead, since you already have a partition table (and a partition). But, like @NobbZ says: make sure you’re using EFI (and boot the installer in EFI mode).

Though, I would not create a second ESP to avoid confusing firmware/bootloaders - rather, as p3 is still unused, delete it and expand your current ESP to ~512MB so you don’t run into space issues.