I am in the process of sourcing an external HD for my Mac to store and edit images using Lightroom and Photoshop.

I shoot with a Canon full-frame camera therefore, the raw image files are in the order of 30 to 40 MB in size depending on the ISO, and some of my PS PSD files are in the order of 500 to 900 MB in size depending on the number of layers.

I intend to edit photos directly form the external HD.

For cost reasons I am not going to purchase a SSD based external HD rather I am minded to purchase an external HD with enterprise class 7200 RPM drives.

My question is; whether the data transfer rates supported by the following interfaces technologies are sufficient to edit images directly on the external HD?

  1. USB-C
  2. USB 3.0
  3. Thunderbolt 3

Or put it another way what data transfer rates that I should look for in products to meet my demands?

Edit 1 The LR catalog and the PS scratch disk will be on the internal SSD.


  • 2
    The only real latency is in the open & save. Everything else is done in RAM & on scratch disk [which will presumably be set to a fast internal SSD]
    – Tetsujin
    Oct 21 '20 at 8:33
  • @Tetsujin Thanks. Yes, you're right. I am over-analyzing!
    – No Clue
    Oct 21 '20 at 10:09
  • @NoClue. Now you do have a clue. ;)-
    – Alaska Man
    Oct 21 '20 at 18:46
  • USB-C is a physical connector specification, not a data transfer speed specification. Oct 21 '20 at 23:13

There will be no discernable difference during editing.

Given that you are not going for an SSD both USB-C and USB 3.0 will deliver roughly the same throughput. Even a high-end standard HDD will not deliver the maximum bandwidth supported by 3.0 in the optical high volume sequential read, so the interface of your choosing will make very little difference.

If it were an SSD, then you can easily exceed USB 3.0 and would go with USB-C instead. There are some hybrid drives with both rotating platters and SSD space which might be worth looking into since you seem to consider the price of pure SSDs too high. Haven't tried those hybrid disks myself though.

Regardless of the media, most processing is done in memory, so it will take quite a bit longer to load your images but once it is fully loaded, the editing speed performance will not be impacted. Exporting will also be slower though. For large very images, the loading time difference is huge between a standard HDD and typical SSD and now that I've gotten 2 NVMEe, it there was another huge leap in performance.

  • Was writing my own answer, but this is pretty much bang on. Only one thing I think should be added for completeness: 3.5" HDDs are typically faster than 2.5" ones (there are exceptions, of course) and higher capacity HDDs are typically faster than lower capacity ones.
    – flolilo
    Oct 21 '20 at 18:35
  • @flolilo Thanks. I am planning to buy a 4TB device and they all have 3.5" drives.
    – No Clue
    Oct 22 '20 at 19:28
  • @Itai Thanks for your answer. I'll look into the hybrid drives that you mentioned.
    – No Clue
    Oct 22 '20 at 19:31

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.