Speed up saving of layered files?

In CS4, on a first generation quad core Mac Pro with 12 gigs of RAM and scratch and all image files on a fast two disk RAID 0, I find that saving psd files with layers is extremely slow.



If I open a 16 bit 12 megapixel D300 raw image from Lightroom into Photoshop, and immediately save it, it takes just 1 to 2 seconds to save the 60 megabyte file. But if I duplicate the background layer and save again, it takes about 15 seconds. If I duplicate two more times so there are four layers, it takes over 30 seconds to re-save the now 286 megabyte file.



Why does this take so long? Are these numbers normal? Is there anything that can be done to speed this up? I can duplicate the file in Finder in less than 4 seconds, so I assume this has nothing to do with disk bandwidth.



And why does saving files have to be modal? If I could start the save then switch over and start working on a different image I really wouldn't care how long it took.
Speed up saving of layered files?
If you save with maximum compatibility, we have to composite (flatten) the document and save that PLUS the layer contents. That takes extra time.



Yes, without major changes, saving has to be modal (due to disk access, error handling, etc.).



Opening a file is decompressing - easy.

Saving a file is compressing - SLOW.
Speed up saving of layered files?
Hmm, but you need to maximize compatibility for the image to work in Lightroom, right?



If saving can not be radically sped up, making the changes to allow non-modal saves sounds well worth doing to me.

Non-modal saves sounds great to me, too.

Unfortunately, I know how much work lies between here and there...

(it's not nearly as easy as it sounds)