How much free storage space do I need for a MacStudio 2TB to run smoothly?

RRRoll wrote:

After trying to keep the 462.5 GB photos library on an external drive

What is an "external drive"? Please specify. There are probably hundreds of thousands of different types of external drives, ranging from a few bytes to many petabytes. Access times range from nanoseconds, to days.

Right now Disk Utility shows 642 GB available on the Mac Studio drive.

In most cases, when the operating system tells you that you have a certain amount of storage "available", that's a total lie.

Disk Utility is one of the few apps that actually does tell you how much free storage you have. But you have to be careful. Disk Utility also reports that bogus "available" storage amount. Ignore that. What does it say up in the graph under "Free"? That "Free" is the only thing that matters.

Can anybody reassure me that this will not be an issue?

Not without more information.

Or should I try something less radical?

You've already dived into the radical areas. Your quest at this point is to get out.

Photos app has bee really tough to use since I bought the new modern fast Mac Studio.

That's probably because you were trying something fancy like storing your photos on that "external drive", whatever it is.

The library is currently on a nice new 4TB internal drive

I thought you just said it was on an external? I'm assuming this is a typo.

Photos app General Settings gives the message "This Library isn't searchable in Spotlight due to its location".

Many of those "nice new" external drives use a "new" technology that is horribly, horribly slow. Manufacturers like it because it's more profitable for them. But "new" external drives can be much, much slower than external drives from only a few years ago. It takes significant research to find an external drive these days that isn't total trash.

All my photos are backed up in iCloud

What does this mean? iCloud is not a backup service. If you have iCloud Photos, then your photos are stored in iCloud and they will be relatively easy to work with.

But iCloud is a sync service, not a backup. All users of iCloud should have at least once device that keeps all iCloud data downloaded and backed up using Time Machine. This is not the default setting.

Will try moving the library this weekend to see if that does the trick. (Am also finding un-used stuff currently stored on my main drive and moving those less important items to the external drive array)

Now it's an external drive "array"? What kind of "array"?

I recommend not trying anything major until you provide more information.

Generally speaking, you'll need at least 100-200 GB of free storage to run comfortably. That's "free", not "available". External drives are fine for backups and archives (another two things that are Not The Same). They really shouldn't be used for anything else. If you tried to save a few hundred dollars on a computer that costs a few thousand, then you may be forced to use an external drive. In that case, make sure it is a fast SSD. Again, those are hard to find. External Samsung SSDs are moderately fast, relatively inexpensive, and readily available. Anything else would need significant research and, even then, you'd be unlikely to do better than the Samsung.

If you have any original documentation or links from those drives, it would be very helpful. Otherwise, something like "4TB Seagate Backup Plus" doesn't have much meaning. "4TB G-Drive" isn't a lot better. If you don't have that, then how else can you describe the drive? Start with the type. Does it spin or not? Spinning is bad in 2024. How big is it? Is it as heavy as a brick, or lighter than that? A big, heavy drive will have a 3.5" hard drive that could be pretty fast (relatively speaking) and reliable. (Note the "could be" qualifier I used there.) Such a drive will have to be plugged into the wall. If it is smaller than that, and/or if it can run without any power other than the USB cable, then it is a 2.5" laptop hard drive. Those things are unsuitable for any purpose. Do not use them.

An external SSD will look a lot like an external 2.5" drive. It will weigh about the same. It will also be bus-powered. Here, look at the cost. How much did you spend for it? Generally, you be spending about $100/TB. So a 4 TB SSD should cost about $400. Anything less than $100 is 2.5" junk. Throw it in the trash. Or maybe now that's 2024, recycle responsibly. In addition to being worthless junk, it's probably full of toxic, environmental damaging materials. But you get the idea.

200GB free should be enough... for awhile anyway, have you considered putting the photos library on a fast external TB3/4 SSD?

OK, best of luck, looking orward to earing the outcome! :)