AWS - drive not detected for G4DN.12XLARGE

Question

I provisioned an AWS machine G4DN.12XLARGE.

G4DN.12XLARGE
 192 GiB RAM  48 vCPUs  900 GB NVMe SSD 4 GPUs  Ubuntu Server 18.04 LTS

I mounted /dev/nvme0n1 which has 838.2GB space.

Disk /dev/nvme0n1: 838.2 GiB, 900000000000 bytes, 1757812500 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Mounted the undetected drives with:

sudo mkfs.ext4  /dev/nvme0n1
sudo mount /dev/nvme0n1 /mnt/volume1

Still /mnt/volume1 is not shown in the df -kh. What am I doing wrong here?

ubuntu@ip-10-0-4-115:/mnt/volume1$ df -kh
Filesystem      Size  Used Avail Use% Mounted on
udev             94G     0   94G   0% /dev
tmpfs            19G  948K   19G   1% /run
/dev/nvme1n1p1  9.7G  1.7G  8.0G  18% /
tmpfs            94G     0   94G   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs            94G     0   94G   0% /sys/fs/cgroup
/dev/loop0       56M   56M     0 100% /snap/core18/2284
/dev/loop1       18M   18M     0 100% /snap/amazon-ssm-agent/1455
/dev/loop2       25M   25M     0 100% /snap/amazon-ssm-agent/4046
/dev/loop3      111M  111M     0 100% /snap/core/12725
tmpfs            19G     0   19G   0% /run/user/1000