New to ecryptfs, what do I need to backup?

Hi,
I am a new ecryptfs user and I am wondering what I need to backup if I setup an encrypted folder pair by hand.
For example, I encrypt the /srv directory on top of itself using sudo mount -t ecryptfs -o ecryptfs_cipher=aes,ecryptfs_key_bytes=16,ecryptfs_passthrough=no,ecryptfs_enable_filename_crypto=yes /srv /srv (see full output below)

I am now interested in what I have to remember. Obviously my passphrase that I entered at first. Do I also need to remember (write down) the FNEK signature?
What about the file /root/.ecryptfs/sig-cache.txt that is mentioned?

I have moved the folder to another VBox and tried it again and it seemed that my passphrase was sufficient. Is the FNEK signature generated from the passphrase + my username or so?

Also: What parts should I not backup online? The Ubuntu tutorials mention a /home/.ecryptfs (when encrypting the home folder = not my case) or similar that needs to be remembered but shouldn't be stored online in order to avoid weakening the encryption. I couldn't find anything similar after running the above command, should I?

I have tried to find this, but the tutorials didn't seem to mention it. I really need to know this before starting backups of my encrypted folder though, obviously.

I hope you understand.
Best,
Matthias

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matthias@matthias-VirtualBox:~$ sudo mount -t ecryptfs -o ecryptfs_cipher=aes,ecryptfs_key_bytes=16,ecryptfs_passthrough=no,ecryptfs_enable_filename_crypto=yes /srv /srv
[sudo] password for matthias:
Passphrase:
Filename Encryption Key (FNEK) Signature [3c2034c2f35aab36]:
Attempting to mount with the following options:
  ecryptfs_unlink_sigs
  ecryptfs_fnek_sig=3c2034c2f35aab36
  ecryptfs_key_bytes=16
  ecryptfs_cipher=aes
  ecryptfs_sig=3c2034c2f35aab36
WARNING: Based on the contents of [/root/.ecryptfs/sig-cache.txt],
it looks like you have never mounted with this key
before. This could mean that you have typed your
passphrase wrong.

Would you like to proceed with the mount (yes/no)? : yes
Would you like to append sig [3c2034c2f35aab36] to
[/root/.ecryptfs/sig-cache.txt]
in order to avoid this warning in the future (yes/no)? : yes
Successfully appended new sig to user sig cache file
Mounted eCryptfs
matthias@matthias-VirtualBox:~$