Why is my vault so much bigger than my aperture library?

You're not alone. My Aperture library is currently 145GB but after setting up the vault and syncing for the first time my Vault is currently at 208GB and growing. I'm not sure where this will go.

Were you ever able to find an answer to this?

I created a vault for the first time yesterday. My photo library is 40GB and my vault is 7MB, that seems very low.

I created a vault for the first time yesterday. My photo library is 40GB and my vault is 7MB, that seems very low.

A vault will always be created empty. You have to update it, to make a backup.

See: http://documentation.apple.com/en/aperture/usermanual/#chapter=27%26section=5

To update an existing vault

1. Do one of the following:
   • Choose Window > Show Vaults (or press Shift-R).
   • Click the Vault Pane button.
2. Select the vault you want to update.
3. Do one of the following:
   • In the Vault pane, choose Update Vault from the Vault Action pop-up menu (with a gear icon).
   • Click the Vault Status button beside the vault name.
4. In the dialog that appears, click the Update button.

Thanks!

This may solve the confusion. I had a similar problem and it has to do with how aperture treats changes to preview sizes. It DOES NOT automatically change all the existing previews to the new specified size. When you change the preview size it just says "Oh OK so you want me to use that size from THIS POINT IN TIME.." To change existing preview sizes you need to select which masters you want to change and then force aperture to regenerate to the new size.. This article explains how..

Aperture: Previews do not update after changing Limit Preview Size Preference - Apple Support

I hope this helps a lot of people as I was looking for an answer for days on this too...

see my answer above Davider. It is just Aperture doing things in it's own little (correct) way...