Extroot configuration on USB disk without wipe

I am using openwrt 22.03.5 on my C2600 router, and I have an external USB SSD connected to it. It has a single ext4 partition, mounted and accessible as /mnt/sda1.
I want to transfer the overlay partition to the disk, but without formatting it.
I could use gparted on my laptop and create the needed partitions without losing data. However I am not sure what partitions to create and their parameters.
I read this guide https://openwrt.org/docs/guide-user/additional-software/extroot_configuration which however has a first step to wipe the disk.
So what would be the equivalent step using gparted without wiping it?

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You just need to create a new partition and specify its name:


The rest instructions should not require modification.

Thanks - I'm trying to understand what the command
parted -s /dev/sda -- mklabel gpt mkpart extroot 2048s -2048s
does exactly so I can create a similar partition with gparted.
I see it creates a gpt label, but I'm confused with the mkpart extroot. Is there an "extroot" file system? Also for the start-end, what do the "2048s" mean?

2048s means start 2048 sectors (approximately 1 MB) from the start of the disk, and -2048s means the partition should go to 2048 sectors before the end of the disk. it's basically allocating the whole disk into one partition.

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The first argument for mkpart is the name of the GPT partition.

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Worked perfectly, thanks!

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