On most linux systems, the table used by the kernel during startup is /etc/fstab and that contains the complete set of filesystems/volumes that the system will have. You may wish to examine the man page, as in "man fstab" as to the format of the file, but basically you're going to put your postgresql volume into this table if it's not already in there. If it is in there already, carefully check that the settings are correct for what you want or expect. Then, you'd probably want to reboot the system to see what the filesystem looks like on a clean startup. At a minimum, every mounted filesystem contains a directory in it called "lost+found", so if you don't see that, it may not be a proper filesystem, or the mount is broken. Without knowing what you're using for the disks, or the O/S, it's hard for me to guess what you really should have or if it's broken.
