Hiya,
I’m running out of space on my 2017 iMac’s 1TB SSD. photo library takes up 500GB… so I’m thinking of moving it to an external drive. Do I need an SSD? Or is a USB connected spinning disk fine? Thoughts?
Also, I’m out of ports… any recommendations for a USB hub? And can I connect drive to that or would it be better to use it for non drives and direct connect the hard drive?
Given how much the SSD prices have dropped in recent years, they definitely are the better option. But a USB connected spinning disk will work, too! Then again: your internal drive is a SSD and you might cringe upon the experience with an external spinning drive connected via USB…
When I still had the iMac I was using this hub:
https://www.amazon.com/-/us/dp/B078859974/
It worked like a charm.
But I think that any USB hub will do its job. 
Regarding power: see below.
It depends. The more power your USB device needs the harder it will be to run it via the hub without external power. There are USB hubs with an external power supply to solve that issue. A spinning drive might work connected to the hub, but it is always better to connect drives directly to the iMac if you have the option when we are talking about USB connections.
Definitely go for the SSD for your photo library. As to power, the hub will work fine for lower power devices like a wired keyboard or data only devices like a printer or scanner connection. Depending on what else is connected, spinning drives can run into power problems when going through a non-powered hub.
If your iMac supports Thunderbolt3, I highly recommend getting a Thunderbolt SSD enclosure and a fast NVMe SSD. It would be just as fast, if not faster, than the internal drive in your iMac.
Is the library for archival purposes or is it the working repository?
I use both a SSD drive for the photo projects I’m working on, and HD for those that I’ve completed.
You’ll appreciate the speed of the SSD if you are often accessing the images. If on the other hand you treat the library like a photo album and only occasionally ‘pull it out’ a HD should be just fine.
Of course, if money is not an issue then go with SSDs!
Have fun!
How is this for an External Photos Library Storage?
Anyone using this particular one.
In the before times I was a frequent traveler, and as one of my hobbies is photography I wanted a portable drive to load image files to. I had been using small HD for that, but as prices have come down I started looking into SSDs. One goal I have is to minimize the weight of my gear. And to that end I decided on a different SanDisk product, the SanDisk 1TB Extreme PRO USB 3.2 Solid State Flash Drive. So far I’ve been happy with this drive. And look forward to using it as I once again start to venture to faraway lands (next up, a birding adventure in Bolivia!).
Note that I use this as temporary storage only. Once home I copy the images to drives connected to my Mac.
If I wasn’t looking for a portable drive I would look for one that connects via Thunderbolt. And for my home setup I use a OWC Thunderbay Mini four drive bay to which I’ve installed a variety of SSD drives that I’ve accumulated over the years.
Here ya go: OWC ThunderBay 4 mini - Thunderbolt 3 - OWC Digital
Note that there is also a Thunderbolt 2 version.
I bought the empty enclosure and added my own drives.
Good luck whatever you decide.
Fantastic and thanks a lot for your information. Appreciate it very much 
another option is to get a Thunderbolt compatible NVMe SSD enclosure. It would be much faster than the SanDisk USB 3.2 . FYI I am using Ugreen. Currently less than $35
I use a Samsonung T5 attached ot my M1 mac mini and I never experienced any lags or problems so far. The SSD “feels” like it is an internal drive.