Assigning scratch disks

SW
Posted By
Steven_Wild
May 9, 2007
Views
358
Replies
4
Status
Closed
Hi,

I will be buying a new PC soon and would like to know the best way to assign scratch disks. I was planning on purchasing 2 drives – (a) approx 160GB for the operating system, programs, etc and (b)approx 320GB for storing files.

Photoshop help provides the following 2 points as a guide to assigning scratch disks –

1. For best performance, scratch disks should be on a different drive than any large files you are editing.

2. Scratch disks should be on a different drive than the one used for virtual memory.

However, these 2 points are in conflict for my situation. Point 1 suggests I should use drive (a) as the scratch disk because my files will be on drive (b). In contrast, Point 2 suggests that I use drive (b) as the scratch disk because virtual memory will be on drive (a).

Without buying a 3rd drive, how should I set up my system? Should I simply have all of my files on the same drive as the operating system and use the other drive as a scratch disk? Seems a bit of a waste buying a 2nd drive just to use as a scratch disk and nothing else.

The Photoshop help also states "you can change the primary scratch disk and designate a second…scratch disk to be used when the primary disk is full". Does this mean that a scratch disk is a waste of time if your main drive is never filled up?

Thanks for any insights you can provide.

Cheers,

Steven
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MD
Michael_D_Sullivan
May 10, 2007
The recommendations regarding location of the scratch files are just that — recommendations. They are not requirements.

To figure out what’s best for you, it would be helpful to know how much RAM you have, how fast your disk drives are, and how much buffering those drives have.

The reasons for the two recommendations are different.

The reason it’s better to put the scratch on a different drive from virtual memory is that if your system has to swap memory to disk often, the scratch files and the pagefile (virtual memory) will need to be accessed and/or written to at the same time, and one or the other will need to wait, causing a very noticeable slowdown. If you have a lot of RAM (e.g., 4 GB, using the /3GB switch in XP), then you won’t be swapping very often, so there won’t be much contention between the scratch file and the pagefile disk activity, making it less likely that there will be a frequent and noticeable performance hit. Also, if one of your drives is much faster than the other and has a large buffer, that would be a good candidate for either the scratch files or the pagefile (or both).

The reason it’s better to put the scratch on a different drive from the image files you will be working on is that when you open or save an image from the same drive as the scratch, the drive has to read one file at the same time as it’s writing the other. Thus, opening and saving files will be slower if both the image file and the scratch file are on the same disk. If a single disk is used for both, but it’s a fast drive and it has a large buffer, the slowdown may be virtually unnoticeable.
SW
Steven_Wild
May 10, 2007
Thanks for the reply Michael,

I don’t know a lot about the technical side, but here are the specs I have:

160GB SATA HDD (3.0Gb/s, 7.2k RPM)
320GB SATA HDD (3.0Gb/s, 7.2k RPM)

Neither have a cache as far as I know. Budget is tight so I won’t be able to buy mega-expensive drives.

At this stage I’m looking at 2GB RAM, but may be able to get 4GB.

From what you say, if I have to compromise, it’s probably better to suffer in the opening/saving of files rather than overall performance slowdown.

Thanks again,

Steven
MD
Michael_D_Sullivan
May 10, 2007
If the two drives are identical in speed, which appears likely, then I’d use the system (usually c:) drive for the OS pagefile and the other drive for the Photoshop scratch. Keep the photos on the second drive, too, not in the default "my pictures" directory that’s layered deep in the structure of the c: drive.
SW
Steven_Wild
May 10, 2007
Thanks again, Michael. Much appreciated.

Cheers,

Steven

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