Lightroom save photos SSD vs. HDD

A raw file is read in when you display it in the Develop module, or to build its preview. That takes a brief moment, and after that, the raw file is not where most read/write happens as you work, so a moderately fast hard drive is good enough for that occasional reading of raw originals.

If you are editing in the Develop module, Lightroom Classic is reading/writing the Camera Raw Cache to cache the edits (since raw originals are not modified by edits), so the Camera Raw Cache location should be on an SSD. You set the location and size of the Camera Raw Cache in Lightroom Classic Preferences / Performance.

If you are not editing an image in the Develop module, Lightroom Classic will display the image’s preview first. And if displaying many thumbnail previews in a grid, it again looks first to see if previews are built. So the first place it reads is wherever the .lrpreviews file is, which is in the folder where the catalog is stored. Because the previews file and catalog are read so frequently, you benefit more by storing their folder on an SSD. If the previews need to be rebuilt, then it does read each actual raw file wherever those are stored, but a hard drive or NAS can be fast enough for that.

One reason to use an SSD for originals is if you frequently capture and edit very high resolution videos that need to be read at a faster data rate than a hard drive or NAS can sustain. But for stills, an SSD is usually not necessary.

External drives used to always be slower than internal, but that is no longer always true. USB 3 (5 or 10 Gigabits per second) is fast enough for SSDs, and Thunderbolt 3 or 4 (40Gb/sec) can connect a high-end NVME SSD in an external enclosure at a data rate that meets or exceeds the built-in storage of many computers.

However, if you pay the highest price for the fastest internal or external storage, you will find that the real world I/O data rate of most applications hardly ever comes close to the maximum theoretical throughput of those devices. USB 3 is fast enough for what most people need, and more than fast enough to connect hard drives with raw files on them.

One thing to add, as this is often overlooked by some, and could really really ruin your day.

Where do you backup your photos?

Keep that in mind.

Nothing to do with editing. Everything to do with the eventual day when that hard drive fails.

Speed of the hard drive will only matter at import, export (including publish service)  and edit in (including PS as well as third party)

So, any hard drive.

Mind you NAS could slow import down if via Copy or Copy as DNG (so import via ADD) and could be notable during a large import. Well export as well, but do you export very many at one time?

During edit, not an issue.

Are you PC or Mac? What os?

If you are using Lightroom Classic the speed of the drive holding your images isn't critical because after the images are imported Lightroom doesn't access them hardly at all. It's good to have your catalog on a good performing hard drive because that is where almost all of the action takes place.

If you are using Lightroom, not Lightroom Classic, your photos are in the cloud so it really doesn't matter. What version of Lightroom are you using?

Personally I have a Promise array of 12TB but use mostly standard USB Drives as Lightroom uses the catalog for most tasks ... I have had catalogs on external drives (separate from images) as well to allow plug and play on any Mac ..

most important for speed is the computer hardware specs.