Liquify & poor performance (scratch drive use)

Question

Hi,
(Firstly, I'm an ex programmer, so fairly technical...)
I've recently been looking into the performance of the liquify filter in Photoshop CS4 11.0.1 on my i7-950, Vista64, 64 bit photoshop, 12Gb RAM. It seems to "stall" for a second or two after certain brush strokes. Other people on the internet have reported similar things.
I've come to the conclusion that the Liquify filter has a fundamental issue, as described below. Firstly, here's what I've noticed:
I'm liquifying a large image (5000 pixels deep) using a large brush (1500 pixels).
When I do a few liquify brush strokes with the push tool, I notice that liquify stalls for a few seconds.
Vista performance monitor tells me that Photoshop is writing a large amount of data to a file on my F drive, which is NOT the drive I've set to be my scratch disk (my scratch disk is Y drive - a fast raptor)
What I believe is happening (this is my guess) is, since Photoshop 7.0, Liquify gained multiple undo states. In the implementation of this, the developers chose to get Liquify to not use the scratch disk that Photoshop does, but instead to choose the largest drive it can find to use to save history states. My evidence for this is that some people with network and USB drives have to disconnect them in order to get liquify to perform well after you lift the mouse button and my F drive is the joint largest I have in my machine. I've also noticed that if you use a 1500 size brush on a SMALL file (like 1500 on it's largest axis) you don't get the same stall - which suggests to me that the history states system saves the entire image (presumably as well as the mesh) in order to speed up the undo.
This problem as described doesn't appear to me anything to do with:
RAM - I have 12Gb on Vista64 and photoshop64 and set photoshop to use 6Gb of that. The photoshop file is a single layer file only at 16bit.
Processor speed - I'm on an i7 950.
OpenGL settings - it's only when I lift the mouse button after several mouse operations that the problem happens. I've also tried switching that off.
History states settings in photoshop - I've tried setting it to one.
I've checked TEMP emvironment variables and virtual memory settings. Neither is specifiying the F drive.
Has anyone else seen this? Can you reproduce it using these steps:
Load a PSD (preferably 16 bit, single layer)
Resize it to over 5000 pixels on it's largest axis.
Start liquify
Change the brush size to 1500 pixels
Do a number of small push brush strokes
After a few, you should notice a small stall
If you can, get the resource monitor up in vista: task manager -> choose "performance" tab -> Click "Resource monitor" button -> open "disk" dropdown -> click on "write b/min" to show you the programs accessing the most disk. This should show you photoshop (liquify presumably) saving a large amount of data to a drive you never told it to use.
I'm quite happy to be wrong with any or all of my guesswork, assumptions and conclusions and would be delighted if anyone has a solution for this - other than the usual "resize, save mesh, load mesh" option to speed up liquify - I have 100 files to liquify and it's just too slow
Thanks everyone in advance for your thoughts
Phil
Finally here's some links which show similar things:
http://www.realgeek.com/forums/photoshop-cs4-liquify-tool-issue-472605.html
http://www.xpertgurus.com/showthread.php?t=171454
http://www.fredmiranda.com/forum/topic/754197/0

Answer 1

Here is what someone else said about the issue:
"When people on here say Photoshop is no longer accessing the scratchdisk as they have lots of ram, are they SURE? I initially thought it was odd when a noise I hadn't noticed before (More than likely due to having loud music on whilst editing) when using alt+click to hide/show all layers was infact my hardrives seeking. It's almost inaudible but I tend to have very sensitive hearing.
So, i'm just working on a large 120 scan building up my layers as you do, and I go to liquify a section of the image. Now it's a large image and even though my PC is fast I don't expect it to absoultely blitz everything I throw at it, and liquify is typically a pretty crap part of Photoshop for speed anyway. So out of curiosity I open up task manager to see what my CPU usage is like.. bouncing along the bottom, jumping upto 25/30% every so often, usually when making larger adjustments, felt happy, and clicked OK.
Something made me open up Resource Monitor and noticed the hardrive jumping upto 180mb/s usage. Expand the view and it is indeed Photoshop absolutely tanning the hardrive. All the while my Ram usage is at around 5GB.
So, if this is indeed normal, a word of advice folks  Invest in a RAID0 scratchdisk volume if you do large edits on large files.. Because photoshop seems to prioritize the scratchdisk before ram in some cases. If this is not normal or doesn't happen to you, please state specs, PS version, settings etc, tar.
For those interested, computer is a 3.2ghz Quad, 16GB of ram, RAID0 array for OS (Which is also the scratchdisk), and Photoshop CS4 64-bit ram usage is set at 70%, Cache Levels 6, History states 20. "
It's from one of the links in my original post.. The thing that I seem to have found that others have not spotted in my investigations is that Liquify is using any disk that it wants and (so far) there doesn't seem to be a way to tell it to use your specified scratch disk.