Inspiring

Answered

Scratch Disk Full Solutions?

Forum|Forum|22 days ago
July 1, 2026
9 replies
212 views

Hi everybody, I have a very big file which I can’t open in PS because the scratch disc is full. The size is 6800 x 4900px. The advice I have found online suggests creating 100GB of space. I have roughly 25GB on my Mac which only has 251GB in total. Is there a way of working out how much space you would need to open and work on a particular file rather than creating 100GB of space if that’s not necessary for that particular file. My file is very big at 6800 x 4900px but it’s only 4 layers. Does anybody have any ideas?

Thanks,
Gareth

Correct answer Conrad_C

Any drive is Mac-compatible as long as you can format it with Apple Disk Utility. Just format it as APFS or Mac OS Extended and you’re good.

Reliability is difficult to predict because it’s a combination of the quality of the drive itself (brand and model), and the enclosure that the drive is inside (controller board, port, cable…).

The practical answer to the reliability question is:

Always assume any type of drive can fail at any time, because that is true.
To guard against that, always maintain at least one (preferably more than one) up-to-date backup of any drive containing data you consider irreplaceable.

The nice thing about a drive used only as a scratch disk is that the data is totally expendable, so you just need one, and you don’t have to back it up. It doesn’t have to be the most reliable because it’s only storing temporary files that are deleted the moment you exit Photoshop.

When people post on the Internet about their drive failing, it’s highly anecdotal…a drive of any brand/model will fail somewhere, we just never know whose. The others will continue working just fine for years. If you must have a quality ranking, a good source would be the reports by Backblaze because they manage thousands of drives for their cloud backup data centers. But, the drives they use for data centers might not be the size and type we would normally plug into our computer.

One very important last thing: You asked about a

100GB external HD

That’s not what you’re shopping for, for several reasons:

100GB is not that much, so if the point is to accommodate larger Photoshop files, aim for 500GB or more although 200+GB might work for most files.
100GB is no longer a common size for an external drive anyway, most trusted brands start at 256GB now.
You don’t want an HD/HDD (hard drive/hard disk drive) today for a scratch disk, you want an SSD (solid state drive). The point of a scratch disk is to help RAM, the fastest kind of memory, and the high speeds of SSDs are much closer to RAM speed than hard drives are. We only used hard drives as scratch disks in the past because that’s all we had. But now that fast SSDs have become common and affordable, they are really the only practical choice for an external Photoshop scratch disk.

So look for an external SSD of 512GB or more. It should support a USB-C transfer speed of at least 10 gigabits (Gb)/second, which is roughly 1000 megabytes (MB) a second. Some examples would be the Samsung T series, Crucial X series, and SSDs by Sandisk or Glyph. All of those are commonly used by creative professionals.

Gareth_WilliamsAuthor

Inspiring

Thanks everybody, that has worked. The word on the street is APFS is better or SDD and Mac OS Extended (Journaled) is better for HDD. I set my external HDD to Mac OS Extended and it works fine. I should have got an SDD and formatted it to APFS really but this will do for now. This video shows how to do both https://www.youtube.com/watch?v=_q8mdhN5Q9U

Thanks again.

Gareth_WilliamsAuthor

Inspiring

Ok, I’ve got an external HD 500GB. How do you add it as a scratch disc? When you go to Photoshop/Preferences/Scratch Discs … you get this dialogue box but the external HD is not there! Even though the external HD is visible on my Desktop. Thanks for your help.

Ged_Traynor

Community Expert

@Gareth_Williams how is the disk formatted

Gareth_WilliamsAuthor

Inspiring

Thanks. I’ll try this tonight. I don’t know what the default format is but I’ll investigate. Thanks again!

Gareth_WilliamsAuthor

Inspiring

Does anybody have any suggestions for a good reliable 100GB external HD? Compatible with Mac and decent quality. Any suggestions? Brands etc? Thanks again.

Conrad_C

Correct answer

Community Expert

Any drive is Mac-compatible as long as you can format it with Apple Disk Utility. Just format it as APFS or Mac OS Extended and you’re good.

Reliability is difficult to predict because it’s a combination of the quality of the drive itself (brand and model), and the enclosure that the drive is inside (controller board, port, cable…).

The practical answer to the reliability question is:

Always assume any type of drive can fail at any time, because that is true.
To guard against that, always maintain at least one (preferably more than one) up-to-date backup of any drive containing data you consider irreplaceable.

The nice thing about a drive used only as a scratch disk is that the data is totally expendable, so you just need one, and you don’t have to back it up. It doesn’t have to be the most reliable because it’s only storing temporary files that are deleted the moment you exit Photoshop.

When people post on the Internet about their drive failing, it’s highly anecdotal…a drive of any brand/model will fail somewhere, we just never know whose. The others will continue working just fine for years. If you must have a quality ranking, a good source would be the reports by Backblaze because they manage thousands of drives for their cloud backup data centers. But, the drives they use for data centers might not be the size and type we would normally plug into our computer.

One very important last thing: You asked about a

100GB external HD

That’s not what you’re shopping for, for several reasons:

100GB is not that much, so if the point is to accommodate larger Photoshop files, aim for 500GB or more although 200+GB might work for most files.
100GB is no longer a common size for an external drive anyway, most trusted brands start at 256GB now.
You don’t want an HD/HDD (hard drive/hard disk drive) today for a scratch disk, you want an SSD (solid state drive). The point of a scratch disk is to help RAM, the fastest kind of memory, and the high speeds of SSDs are much closer to RAM speed than hard drives are. We only used hard drives as scratch disks in the past because that’s all we had. But now that fast SSDs have become common and affordable, they are really the only practical choice for an external Photoshop scratch disk.

So look for an external SSD of 512GB or more. It should support a USB-C transfer speed of at least 10 gigabits (Gb)/second, which is roughly 1000 megabytes (MB) a second. Some examples would be the Samsung T series, Crucial X series, and SSDs by Sandisk or Glyph. All of those are commonly used by creative professionals.

D Fosse

Community Expert

Always assume any type of drive can fail at any time

That is so true. I’ve been in so many discussions about drive reliability, and I’ve kept saying that the whole discussion is pointless. You need to be prepared for drive failure at any time, and that’s the end of that discussion.

Some manufacturers and product lines may have better statistics, but that’s all it is. That has no predictive value on an individual level. The only thing you can be sure of is that it will happen when you least expect it.

L

lisa_9817

Known Participant

Yes, to the 100GB scratch disk. Ged_Traynor suggestion in spot on. 100 GB external hard drive should work well.

Conrad_C

Community Expert

My own guideline is to keep 100GB or more free on my MacBook Pro, 200GB if I can manage it. If it gets below 50GB free, I consider that an emergency and I have to get stuff off the internal storage. In my mind 25GB is basically the same as no free space.

It’s not just because of Photoshop. Many applications, and macOS, need enough free space for various temp/cache files, swap files, the macOS sleep image, the Time Machine local snapshots…

It’s understandable that it’s difficult if your Mac has just 256GB of internal storage. 256GB is fine for things like office documents where the documents can be just a few MB and the applications don’t really create temp files. But 256GB can be a major challenge when working with creative applications (not just by Adobe) that have to buffer and cache large numbers of pixels to maintain high graphics performance.

When I’m in your situation, what I do is simple: Grab a spare external SSD with lots of free space (like 500GB or more free), and plug it in. Then, in Photoshop Preferences, Scratch Disks, assign it as a scratch disk, and also set it as the primary scratch disk (at the top of the list) so that Photoshop uses it before it uses the Mac’s internal storage. I’ve been doing that for over 20 years any time Photoshop wants to make a scratch file larger than the free space on my Mac laptop. (My first external scratch disk had a FireWire port.)

Is there a way of working out how much space you would need to open and work on a particular file

There isn’t an easy formula, but having used Photoshop for many years I’d say the factors can include:

The number of pixels in the image, so a 12 megapixel phone camera image needs a much smaller scratch file than a 50 megapixel image from a pro camera.
The bit depth of the image
The number of layers
The number of History states, so one way to reduce the scratch file size is to reduce the number of History states retained in Photoshop Preferences, Performance panel, History States option

The smaller those numbers are, the more likely the scratch file will be under 100GB. The larger those numbers are, the more likely the scratch file can be several hundred GB, like for a panorama.

Gareth_WilliamsAuthor

Inspiring

I’ve got an external HD with a Firewire port. Old-school! That one has a dodgy input connection these days. I think I need to invest in another one. Thanks for your post.

D Fosse

Community Expert

Just to sum up the other correct answers here: You need to clear out more space ASAP! 25 GB can be gone in less than a minute, and then your whole machine may freeze up.

You might get away with 100 GB, but my standard recommendation is 500 just to be safe. I have several TB.

Here’s what you need to know: Raster image editing eats disk space. Every history state for every open document can potentially add the full uncompressed file size to the scratch file. Plus some overhead. With the current default of 50 history states, that quickly adds up. In addition, the operating system needs free space for regular routine maintenance. And then there’s the system pagefile, which is used for smart objects and many advanced AI-based functions in Photoshop.

c.pfaffenbichler

Community Expert

Do you have a second hard disk you could use as a secondary scratch disk?

What have you done for Photoshop-performance so far?

For example how many History steps are you using?

Gareth_WilliamsAuthor

Inspiring

I put the history states down to 9 from 50. It didn’t make any difference though!

L

lisa_9817

Known Participant

I agree with c.pfaffenbichler, get an external hard drive and set it up as your scratch disk.

I had to do the same thing.

Trevor.Dennis

Community Expert

Hi Gareth. When I start Photoshop with nothing open it creates a just short of 5GB temp file on the scratch drive.

I have opened a Canon 5DS RAW file which is 8688px X 5792px

and the temp file has increased 7Gb

Copy the layer and add a bunch of noise and it increases to 10Gb.

I’m guessing that it is not that simple though. Your Mac probably needs drive space for some sort of Page file. This is WinDirStat which is free and incredibly useful. It shows Windows 11 has reserved 26.7Gb for the Windows Page file. That big blue rectangle top left corner is my iPhone backup and 207Gb !! I might have to do something about that.

Can anyone recommend a decent WinDirStat alternative for Mac? If we can find one you use it to find large blocks of data, and then research to see if you can relocate that data to another drive. That will make your system work better.

Or look for info on how to go straight to saving drive space.

Note: I am an occasional Mac user, and have very little expertise, so be sure to do your research

How to free up disk space on Mac: a complete cleanup guide

Conrad_C

Community Expert

Can anyone recommend a decent WinDirStat alternative for Mac?

GrandPerspective is an old standby for this kind of thing…

https://grandperspectiv.sourceforge.net

Disk Inventory X is another one that goes way back, but I'm not sure how compatible it is with the latest macOS.

Ged_Traynor

Community Expert

@Gareth_Williams I wouldn’t consider a file size of 6800 x 4900px with 4 layers to be very big, although it depends on what the layers contain.

I opened a 16320 * 7532px file with 4 layers, 2 of which I converted to smart objects and the scratch disk size is only 7GB, if I add a few type layers, the scratch disk size increases to about 10GB

The advice to have a 100GB or more for the scratch disk still stands though.

Gareth_WilliamsAuthor

Inspiring

Your file is much bigger than mine. You must have a lot of free space to open that! I don’t think what is in the layers makes any difference to the size but for everybody’s information, one layer is an image, the other three are text and vector shapes all exported from illustrator. I think I need to invest in an external HD for sure!

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