Performance of internal vs external ssd scratch

[erikreitan]

Hi

I´m buying a 4.2 ghz imac with 64gb of ram, and am trying to decide on how to solve the issue of scratch disk in PS. 

I work with fairly large files, PhaseOne, large composites and stitch files, file sizes between 3-8 gb etc

My alternatives for scratch disk are:

1) getting a 1tb external Sandisk 900 and stick with the 512gb internal SSD that comes with the Imac

2) upgrading the internal SSD on the imac to 1TB and partition it something like 200gb/800gb with 800gb for dedicated PS scratch

The first alternative gives me less storage on the internal drive and is more expensive, but gives a larger scratch disk, the second could possibly give better overall performance.

Which alternative is more preferable? And how much of a performance boost does an internal drive provide vs an external? Are there better alternatives when it comes to external drives for scratch?

[Trevor.Dennis · Accepted solution]

I don't think you'd need to partition an SSD, for the same reason we don't defrag SSDs.  They handle all that organising the blocks of data so much better than a mechanical HDD. 

I have a Windows system with 64Gb of RAM, and so far, Photoshop has never once created a Temporary file on the Scratch drive, which is a 512Gb Samsung 960PRO NVMe drive. The biggest document I tested this with was a 30,000 x 30,000 pixel document we use for testing performance (by timing a 5000 pixel brush with 1% spacing to move from corner to corner (11 seconds on my i9-7900X system)

I don't worry about reserving drives for Scratch space when using an SSD anyway, because of how they work.

But if you do use an external drive, how will it be connected.  I am out of date with Mac stuff, and never knew much anyway, but I remember reading that Thunderbolt was uber fast.  My gut feeling, has for several years now, told me that anything that requires a lot of disk activity slows Photoshop down.  Even 4000 pixel square documents can get into lag with 150 layers — especially when you start nesting Smart Objects.

We'd appreciate it if you come back and give us a heads up on how your new Mac does with Photoshop, and maybe try the 30k pixel 5k pixel brush test, but with 64Gb RAM, I really don't think you have too much to worry about.

[erikreitan]

Thanks, it seems that going with an internal drive to begin with is the best choice, and then I can always add an external one if this is not sufficient.

Will report back with experiences when the time comes!