Size of filesystem doesn't match up with multiple SSDs

I have a new box with two 512GB NVMe SSDs. The output of lsblk

NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
loop0 7:0 0 61.9M 1 loop /snap/core20/1434
loop1 7:1 0 67.8M 1 loop /snap/lxd/22753
loop2 7:2 0 44.7M 1 loop /snap/snapd/15534
nvme0n1 259:0 0 477G 0 disk
├─nvme0n1p1 259:1 0 511M 0 part
├─nvme0n1p2 259:2 0 476G 0 part
│ └─md127 9:127 0 475.8G 0 raid1 /
├─nvme0n1p3 259:3 0 512M 0 part [SWAP]
└─nvme0n1p4 259:4 0 2M 0 part
nvme1n1 259:5 0 477G 0 disk
├─nvme1n1p1 259:6 0 511M 0 part /boot/efi
├─nvme1n1p2 259:7 0 476G 0 part
│ └─md127 9:127 0 475.8G 0 raid1 /
└─nvme1n1p3 259:8 0 512M 0 part [SWAP]

shows that they are both mounted on /.

However, when running df -h I get

Filesystem Size Used Avail Use% Mounted on
udev 16G 0 16G 0% /dev
tmpfs 3.2G 1.8M 3.2G 1% /run
/dev/md127 469G 445G 164M 100% /
tmpfs 16G 0 16G 0% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 16G 0 16G 0% /sys/fs/cgroup
/dev/loop0 62M 62M 0 100% /snap/core20/1434
/dev/loop1 68M 68M 0 100% /snap/lxd/22753
/dev/loop2 45M 45M 0 100% /snap/snapd/15534
/dev/nvme1n1p1 511M 5.3M 506M 2% /boot/efi
tmpfs 3.2G 0 3.2G 0% /run/user/1000

which shows that I only have the space of one of these SSDs.

How can I get the filesystem to use the memory from both SSDs, so 1TB in total?

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