Techniques to set up Adobe Photoshop scratch disks to increase swap file access speeds.

Setting up Photoshop scratch disks

What is the best way to optimize Photoshop scratch disks?

Scratch disks are used by Adobe Photoshop to store temporary swap, or virtual, memory when it has used up available RAM. There are many ways of setting up scratch disks for Photoshop and not all of them are appropriate for all users or systems.

Allowing Photoshop its own area of contiguous free space to use as a scratch disk is the ideal the way to go. However, if you are working with just the one internal hard disk, it is best not to use a partition as a scratch disk.

For single drive machines (such as portables), Photoshop will work faster if it is able to pick where to put the scratch disk data. However, if two partitions are used, it is best to put the operating system on the first (faster) partition and to also select this as the scratch disk in the Photoshop preferences.

With desktop computers it is easy to add a separate physical hard drive to use as a dedicated scratch disk. For the most part it is best to install an internal disk, rather than to rely on external drives. A number of options are available and the choice is limited mainly by cost and requirement.

High end Photoshop users who work with large files often recommend the use of Redundant Array of Independent Disks (RAID 0 array, or striped array). RAID 0 is a method of formatting two or more hard disks into a single volume so that data can be accessed more quickly. Obviously this is more expensive than using a single hard disk and designers will need to decide whether the speed benefit is enough to justify the cost.

The disk connection method is also worth considering. SCSI is still considered by many pros to be the fastest (most computer system come with SATA or ATA), although it is getting competition from Firewire 800. Some portable computer users will use a fast external hard drive as a scratch disk. This will work best if the laptop has at least a Firewire 400 connection, if not Firewire 800. However, it is not advisable to use removable media, such as Zip or Jaz drives, as scratch disks. Network drives should never be used, as it will really upset your IT manager if several gigabytes of data are written to network volumes.

Hard disk speed is also an important factor and disks with speeds 10,000rpm or even 15,000 rpm are worth considering. Most standard PCs come with internal disks of 7200rpm and portables will generally be 5400rpm and sometimes even as slow as 4200rpm.