Adobe has some tips on how to setup your scratch disk to optimize photoshop performance (I assume you are referring to photoshop, since you posted in General Photography Talk) :
When Photoshop needs more memory than that available, it uses a portion of the hard drive as virtual memory or scratch disks. This process allows you to work with large image changes that exceed the capacity of your system RAM. The more hard-drive space available and the faster the drive access speed, the more efficient this process becomes. As a rule of thumb, aim for hard drives with faster disk rotation (usually classified in RPM) and faster read/write speeds. If you have the budget, then take a look at SSDs. Ideally, you should use a dedicated, empty hard drive that is not your startup disk, but if empty drives are not possible, at least make sure that the free space on your scratch disks is not fragmented.
To view or adjust your scratch disk settings, choose Photoshop/Edit > Preferences > Performance and look at the scratch disks area in the middle of the panel. The panel will show you a list of all hard drives attached to your system, and you can arrange both the order in which Photoshop uses them and which drives to use at all. Up to 64EB of scratch disk space is supported on a total of four volumes (an exabyte is equal to 1 billion gigabytes). If you have more than one drive and you want to include your startup drive as part of the scratch disk, be sure it is last in order for maximum efficiency. You should also use hard drives with fast access (read/ write) speeds and as a general rule avoid removable or networked drives, which cause performance lags due to the time required for communication to and from the disks.
A scratch disk is any drive or drive partition with free memory. By default, Photoshop uses the hard drive on which the operating system is installed as the primary scratch disk.
For best performance, connect the scratch disks to a compatible port that has the highest bandwidth limit of all the available ports. The bandwidth limits for various ports are listed below:
Thunderbolt = 10GB/sec
eSATA = 600MB/sec
PCIe = 500MB/sec
USB3 = 400MB/sec
USB2 = 35MB/sec
To improve performance, set the scratch disk to a defragmented hard disk that has plenty of unused space and fast read/write speeds. If you have more than one hard drive, you can specify additional scratch disks. Photoshop supports up to 64 exabytes of scratch disk space on up to four volumes. (An exabyte equals 1 billion GB.)
If your startup disk is a hard disk, as opposed to a solid-state disk (SSD), try using a different hard disk for your primary scratch disk. An SSD, on the other hand, performs well as both the primary startup and scratch disk. In fact, using an SSD is probably better than using a separate hard disk as your primary scratch disk.
The following guidelines can help you assign and manage your scratch disks:
Scratch disks should be on a different drive than any large files you are editing.
Scratch disks should be on a different drive than the one your operating system uses for virtual memory.
RAID disks/disk arrays are good choices for dedicated scratch disk volumes.
Welcome Well, those are practical and clear guidelines, which I find useful. Knowing what users have doesn't help me at all, because everyone's usage requirements, budgets, needs/wants all differ. But sure, up to you
My setup below, hope this helps. Scratch disk #1 is a 7200rpm HDD, disk #2 is a SSD.
I personally have a different setup. In terms of scratch disk, I have 1 of my old Samsung 250GB ( a 3 years old 850 EVO ) dedicated as scratch disk for CC, Page Files for OS, cache disk for ACR / Bridge and also Temp folder for PTGui Pro.
I used another Samsung 250GB for Windows and Sandisk 960GB for data.
- Some information on my work load is mostly huge HDR panorama editing, so using quite a lot of DDR and Scratch disks.