Photoshop CC Scratch Disk size

[Guest]

Hi Guys,

I'm considering the purchase a dedicated Scratch Disk [SD] for when editing. I currently have 32 GB of RAM and a 6 core processor, so I'm not struggling for speed or memory at this time. The question I have is would PS benefit from  a 128GB SSD dedicated to SD use.

I assumed it would only be used if the available RAM was already commandeered but searching the Forums,  it seems many think Photoshop uses the SD for other purposes as well ?

PS requires that a SD is defined in the Preferences area but that doesn't mean it's being used. I rarely see the Performance % [bottom left of PS work area] dip below 100%.

Any thoughts on this please as I don't want to waste £100 .

LJ

[JJMack]

LJH wrote:

Hi Guys,

I assumed it would only be used if the available RAM was already commandeered but searching the Forums,  it seems many think Photoshop uses the SD for other purposes as well ?

LJ

That assumption would not be correct.  However a dedicated SSD will help greatly.  On my workstation I have two 6 core xeons  processors and 40GB  of RAM  Photoshop is configured so it can use all RAM however  I have only seen Photoshop use more the 10GB of RAM  a couple of times but have see it use more the 100GB of scratch disk space.  Also if  Photoshop allocate a resource for use it will not return it to the system till Photoshop is closed down. Even if it not using the resource for it done with what it was being used for.  Photoshop will hold on to the resource just in case it may need it.  Photoshop manages the resources it allocates from your system.  If I look at my Ram  and disk usage with Photoshop not started then just start Photoshop I will see Photoshop grab  1/2GB of ram and 4GB of temp space.  While Photoshop can consume a lot of system resource it may not use was much as you may think it will. After starting Photoshop just now. I use a script I wrote to layout 36 4x6 image into a document to be printed on roll paper.  The 36 image all were 5MP jpeg camera images.   Each 5MP jpeg file was open and resized to  4x6 at 300dpi copied and pasted into the print document and the jpeg image document closed.  The 36 masked layer document created was 4800px x 16200.   Photoshop allocated an additional 2GB of RAM and 3GB of scratch space processing the 36 jpeg files into a single print document. During  the process only two document were ever open ate the same time.  The Print document and one image document. The with the print document still open in Photoshop I open the 36 5MP jpeg images. Photoshop allocated and additional 1GB of RAM and 1GB of temp space.  My machine still had 30GB of RAM free. Photoshop was using around 3GB of RAM and 8GB of Temp with 37 Document open 36 8bit 5MP images and 1 78Mp layer .document.

Repeated test use 36 16MP RAW file  Raw File I open in 16bit color after the 8Bit print document was created I opener 16 16MP RAW file 16bit RGM document Photoshop was using 7GB ram ad 16GB temp space.

[Guest]

This is interesting JJmack. Good to see that an actual situation has been used to show that Photoshop does indeed use system resource, outside the available RAM. What is alarming is that Adobe actually state that Photoshop will use RAM first, before the available scratch disk allowance. Perhaps it does but only for less demanding tasks.

I suspect there is an algorithm running within Photoshop that calculates the required space to fulfill a requirement [such as yours]. If it assumes [rightly or not] that this may be greater than the available RAM, it secures the amount of contiguous space on the Scratch Disk and uses it. Makes sense I guess.

Seems like my £100 could be well spent.

Many Thanks.

LJ

[Jeff Schewe · Accepted solution]

LJH wrote:

This is interesting JJmack. Good to see that an actual situation has been used to show that Photoshop does indeed use system resource, outside the available RAM. What is alarming is that Adobe actually state that Photoshop will use RAM first, before the available scratch disk allowance. Perhaps it does but only for less demanding tasks.

The way that Photoshop virtual memory (scratch disk) works is a SD is allocated upon launch.  Depending on how much ram you have, the SD temp file can be as large as the ram allocated to Photoshop. This is done so that the "ram first" use can seamlessly transition to ram + SD. Once that initial SD is set up, opening images also increases the SD allocation (in the background as long as the image fits in ram). Open multiple images also increases SD allocation. Also note that History states adds to the SD allocation. Each history state is written (in the background) to the SD.

As log as your efficiency stays at 100%, the SD is only written to as needed, in the background. Once your efficiency starts to drop, tat background writing turns into a foreground opperation and when that happens, Photoshop slows down. Below 80% is noticeably slower, if you drop further, it gets even worse..

And, actually,Photoshop does indeed relinquish allocated ram at the request of the OS. They way hat works varies depending on Mac & Windows. Reallocation can take a while on either OS and it only happens when another apps requests ram from the OS. So, it can look like Photoshop is hoarding allocated ram but it's not...it just keeps it unless the OS demands it back–and it's not immediate either.

[Guest]

Thanks Jeff. In view of what's been discussed in this thread, I think I'll invest in 128 Gb of SSD RAM for the Scratch Disk. Nothing lost and it gives me a nice buffer should it be needed [actually used that is].

I've read both your Digital Print/Negative books by the way. Excellent works. Makes a change to read content that isn't just a conveyor belt of ' nice shots' with little real theory behind the process. Well done, a breath of fresh air.

[bagonterman]

Do you think that increasing the scratch disk size on a virtual machine would help increase performance. We have some virtual machines running CC15 that run really slow. Right now the scratch disk size is 27.44 GB.

[JJMack]

I do not think changing just the size would help.  Changing the Scratch space real device type and connection type may help. You should look at the configurations of your real Machine Hardware and OS and your virtual machine configuration mapping to you real hardware devices.  You should expect Photoshop to run slower in a virtual machine. However, if your running a Linux machine it would your only option. IMO it would be better to have a dedicated real machine for Photoshop.

SSD and faster Processors

[bagonterman]

Thank you for the reply Mack. The strategy for now is to create more virtuals to make up for the loss of performance. I don't like it but I don't have enough say in the matter. I was just hoping I could find a better solution.