Your Mac has a finite amount of RAM. Many design applications such as Photoshop, Premiere, After Effects, Krita and the like will often use all available memory at its disposal. And, more often than not, these design programs may require even more RAM than what your Mac can supply.
In such an event, a program like Photoshop will use your Mac’s internal storage as a scratch disk. Think of a scratch disk as dedicated temporary storage for portions of your documents that don’t fit into the memory or RAM of your machine.
Many general users can get by with using their Mac’s internal storage as a scratch disk. It makes sense if your Mac’s drive is capacious and you have a lot of free space.
But, if you’re in the habit of using your Mac’s internal storage for holding applications, data, and the like, you may not have as much space for your scratch disk. In fact, if you encounter a “Scratch Disk Full” error, your Mac is telling you that you are running out of storage space on your internal storage device.
To avoid such a scenario, I recommend having a dedicated scratch disk that your Mac can use. What you’ll need is at least one NVME M.2 drive with 500GB or more capacity and a USB-C or Thunderbolt enclosure. You can get both or just an enclosure if you already have an M.2 drive with the extremely speedy OWC Express 1M2 and Express 1M2 80G.
The Express 1M2 offers USB4/Thunderbolt 4-level speeds up to 3,836 MB/s. The Express 1M2 80G doubles the bandwidth thanks to USB4 v2, providing speeds over 6,000 MB/s. Faster data throughput is crucial when it comes to scratch disks as it means no lag or data thrashing. For this reason, you’ll want to avoid using platter-based (aka traditional) hard drives. Going with either Express 1M2 drive makes this step a no-brainer.
Once you’ve got the NVME drive inside its enclosure, the next step is to connect it to your Mac and format the new drive using Disk Utility. Give your dedicated scratch disk a name (I typically call it “Scratch Master”) and format it as an APFS volume.
Next, you’ll need to tell your favorite design applications where your new scratch disk is located at. In Photoshop’s settings, for example, go to Photoshop > Settings > Scratch Disk and select your newly formatted drive. Photoshop will allow for multiple scratch disks. Scratch disk drives are prioritized from 1 to 7, should you have more than one free volume you wish to use for that purpose. In my experience, having one dedicated scratch disk for multiple applications is more than enough. (Each application will write to a separate folder on your scratch disk.)
For Premiere, you’ll want to visit Settings > Media Cache and change the location of the Media Cache files to a folder on your scratch disk. I also have the Media Cache database point to the scratch disk as well.
The big advantage of having a dedicated scratch disk is optimal performance. You can open and work with larger files with ease, and not have to worry about whether you are encroaching on the limits of your internal drive’s available free space (thereby risking data corruption / sluggish performance).
For the ultimate scratch disk setup, don’t miss the OWC Express 1M2 and Express 1M2 80G.
Excellent advice. I have this exact enclosure and it’s fantastic. The only thing I would add is to format the drive as ExFat! With Blackmagic Disk Speed Test I get a consistent ~2200MB/s WRITE and ~2700MB/s READ as ExFat. However, if the cache drive is APFS (unencrypted) the results are dramatically inconsistent. Sometimes it will be a little faster than the ExFat, and other times it will drop down to ~800MB/s for read or write.