To add an additional disk/volume on your OVH public cloud, you need to follow some steps.

First, identify your new disk :

fdisk -l

You can have different output depending of your system (sd{x}, vd{x}).

Then create a new partition :

# parted /dev/{{disk}}
mktable gpt
mkpart primary ext4 512 100%
quit

Format it :

mkfs -t ext4 -L rootfs /dev/{{disk}}1

Mount :

mount /dev/{{disk}}1 /mnt

Let’s make it peristent, we need UUID. To get block ID.

# blkid
/dev/sdb1: LABEL="rootfs" UUID="6b75bbb4-b311-4b9d-a8fd-6e6ff23c401f" TYPE="ext4" PARTLABEL="primary" 
PARTUUID="e20dc227-9d10-41c4-a714-2fb53d190c11"
/dev/sda1: UUID="9abb590f-8a5e-496f-ad2a-2c877415bdc5" TYPE="ext4" PARTUUID="71036eb1-01"

Add it on /etc/fstab file with mount information.

# vim /etc/fstab
[...]
UUID=6b75bbb4-b311-4b9d-a8fd-6e6ff23c401f /mnt ext4 errors=remount-ro,discard 0 1

Confirm good configuration with one reboot.