I just wonder..

Look into the Aperture library at the size of the folders "Previews", "Masters", "Thumbnails", iPod Photo Cache. trl-click the Aperture library and use "Show Package Contents". With your Preview settings the "Previews" folder should be about 25GB, the Thumbnails perhaps the same size. Are you syncing with iTunes? You may have a huge iPod Photo Cache: iTunes: Understanding the iPod Photo Cache folder

Re "Previews": When did you change the Preview settings? This will not change previews that already have been created, only new previews. To be sure, all images have small previews, use the command "Photos > Delete Previews" and then "Photos > Update Previews", while holding down the options key.

But 1280x1280 is really tiny for previews. I prefer the previews to be at least as large as the display, so that they can be used a screensaver and the desktop wallpaper.

There is a simple, free, program that let's you do the analysis Léonie recommends: Omni Disk Sweeper.

Your numbers don't seem out-of-line. The analysis will break the total down and show you the constituent parts.

(Sent from my magic glass.)

The iMovie Thumbnails will be created, whenever you are accessing the Aperture Library from iMovie 9.0.9. If you delete them, they will be recreated and that takes a lot of time. You can only avoid them by deleting all videos from Aperture and only keeping them in iMovie, or by using the newer iMovie 10.0. That version does not create thumbnails for the movies in the Aperture library, as far as I can see with iMovie 10.0 and Aperture 3.5.1. What versions are you using?

Damien,

are 128 GB APerture library really a problem? Do you have a small internal SSD drive? Then I'd move the complete Aperture library to your external drive and not just the original image files.

Aperture needs the thumbnails for speedy browsing, and I see no way to decrease the file size for them.

Léonie

Aperture does it's housekeeping in the background. Let it run unmolested overnight (make sure your machine is plugged in and set to not sleep) and take a look at the numbers again in the morning.

I would also repair your database. Details are on Apple's Aperture trouble-shooting page. Do this before trying to slim your Library further.

Have you un-checked "New projects automatically generate previews" on "Aperture ▹ Preferences ▹ Previews"?

Are any of your Images shared outside of Aperture (Facebook, Flickr, etc.)?

There are other things to check, but as Léonie wisely points out, for most users the advantages of letting Aperture run the way it wants usually outweigh the need for a smaller Library.

Nonetheless, 800 KB per Image for thumbnails is high.

1. I would check whether your database is holding thumbnails for faces. Show the Library package contents in Finder, double-click the "Thumbnails" folder to make it topmost in the current window, and search for "face" in the filename.
2. Drill all the down to the bottom of a few roots of "Thumbnails". What do you find?

NB: do not change or delete anything in your Library package. If you do, you are likely to corrupt your Library.

With the other apps, I am almost full now. Would you think that having it on the 2To FW800 would be much detrimental, speed wise ?

If your system drive is almost full, this will slow down the system, and you do indeed need to free space. Moving your library to a Firewire volume should work. This would have the added advantage that you could turn it into a managed library again.

But just try it yourself. COpy the library to the external drive and open it in Aperture. Try a few edits. Do you notice any additional slowness?

Other than initial Library load time, I don't think you notice much difference between a Thunderbolt or USB-3 drive and an SSD. (Whereas, as you've found, the difference between an SSD and FW800 is apparent.)

I'm not sure you have that much of a choice. You need to free up space on your system drive. I suggest -- and I think others will agree -- that you _always_ leave 40 or more GB free. Stalling or crashing your system, and/or corrupting your Library, should be avoided, even at the cost of a small reduction in performance.

Keep us posted on what you do.