First, don't mount disks using /dev/sda and /dev/sdc. This will cause problems later as these are not unique. Use UUIDs or /dev/disk/by-id/yourdiskID in your fstab instead.
Then PVE needs to know how to use those disks. For that you need to create storages in PVE. For example by creating a Directory storage via "Datacenter -> Storage -> Add -> Directory". And don't forget to set the "is_mountpoint" option via CLI or this might break your PVE installation later in case mounting ever fails (which isn't uncommon when using "/dev/sdX"). So for example: pvesm set YourStorageID --is_mountpoint yes