Finder extremely slow when opening large folders

You need to meet us halfway here. What do you want from us? You asked if this was expected behaviour and asked for workarounds. We answered truthfully to the best of our knowledge. But that's not good enough?

On these forums, I regularly see people complain about network performance on macOS. These questions are not like your question. They always follow a very precise pattern. They do not deviate. In each case, macOS was the absolute epitome of networking power and speed, besting all other operating systems, right up until the release of macOS 26.1, or macOS 26.0, or macOS 15.7.1, or macOS 15.6, etc.

My answer is always the same. The last time I used macOS on a network was 2017. We had literally unlimited funds for hardware and support staff. And the support staff was uncommonly competent. macOS was an absolute dog. It would regularly lock up the system due to icon previews. Attempting to open a file on the server was guaranteed corruption. The only way to use it was to treat it like it was an FTP server. Copy a file locally, edit it on the hard drive, copy it back to the server. So I'm always skeptical that Apple somehow managed to overcome that only to break it all every year, and then apparently fix it every year.

I just so happen to have an Ubuntu server right here. I still have my old clip art package from like 20 years ago. Make I can actually use it for something. I copied all of the JPG images into one folder of 67k images. Then I opened that on macOS Finder (Sequoia, actually). It locked up the operating system requiring a reboot.

So then I started smaller and added more files:

3000 files - Linux ls 0.086s, macOS smb ls 35s - 1.2s, Ubuntu file browser ~1.0s, macOS smb Finder 3s

10000 files - Linux ls 0.279s, macOS smb ls ~112s - 3.2s, Ubuntu file browser ~3.0s, macOS smb Finder 8s

20000 files - Linux ls 0.570s, macOS smb ls ~180s - 6s, Ubuntu file browser ~4s, macOS smb Finder 2s

Note that all Linux and Ubuntu values are local disk access, not samba. My experiences with similar problems on Linux years ago were on a large NFS network.

Note: After 3000 files, I made a point to turn off icon previews in Finder > View > Show View options for this folder. Before I did this, I noticed that it behaved differently than I remembered. It didn't seem to load all icon previews at once. Instead, it would load them on demand, as I scrolled down. It was a poor user experience with heavy lag. Turning off icon previews eliminated the lag.

The command line interface behaved very strangely. The first time I got a listing in Terminal, it was horribly slow. But subsequent attempts were much faster.

Finder seems to rely very heavily on caches. After putting 20,000 files into this folder, Finder responded instantly, but said there were only 10,000 files there. It was only after I let Terminal ls grind out for 3 minutes did Finder show all 20,000 files.

You might want to try creating a new folder on your server with only a few files. Open that with Finder and turn off icon previews. Then move the rest of those 20,000 files there.

After all of this, I opened a fresh connection to the server with my Tahoe test machine and loaded that directory in the Finder. It took about 15 seconds to load. It was a little bit laggy. It took about 3 attempts to eject the server because it claimed that "Finder was using it". (It wasn't).

Of course, there are no icon previews. I can still do QuickLook previews with the spacebar. If my experience from 2017 is any guide, that will destabilize the system eventually.

I'm afraid that's as good as it gets. If that isn't good enough, then you'll just have to use Windows.

PS: Most tests conducted with a 2021 16" MacBook Pro with 32 GB RAM on a 1,200 mbps wireless network. The Tahoe machine is a 2023 M2 MacBook Air with 16 GB RAM on the same network. Linux machine is an ancient Acer AMD desktop. But it does have a wired 10 Gbit connection to the network.

Yida_Li wrote:

This is my photo backup. I keep all the photos together so I can browse through my memories seamlessly, just like in the Photos app.

Why not just use the Photos app itself? Isn't that what it was designed for?

If I were to split them into separate folders, such as by month, then every time I want to look back at my memories, I would need to keep opening and closing folders, which is very inconvenient.

Try using the column view. You don't have to open or close any folders that way.

What confuses me is that Finder struggles to open this folder, yet in Terminal I can run a single ls command and immediately get a list of all ~20,000 filenames. In fact, I even wrote a small file browser myself just now with under 100 lines of code, and it can list all 20,000 filenames immediately. That makes me wonder what Finder is doing differently to cause such long delays.

I can tell you what Finder is doing differently. Finder is opening each file, building an icon preview of the file, and caching it. If you add that feature to your file browser, you'll find it running much more slowly too. And I'm sure it's doing more than that. But it's the thumbnails that take most of the effort.

Yida_Li wrote:

I also tried reducing the size of the folder to around 500 items, and it still took about 15 seconds to open, which is also extremely slow, even though much better than 1 hour.

So this makes we think there is an issue in your setup. I have a folder with 773 image files (jpg), see below ... this on a 2019 MacBook Pro (Intel), which is a fairly old and not very fast laptop with only 16 GB memory. When I open this folder it opens in much less than 1 second, so fast I cannot even measure it. Your 500-file folder opens in 15 seconds, that seems like an ETERNITY. Why might it be so slow?

If this is with an external drive, how is that drive formatted? What model/make drive is it?

For the NAS connection, some operations over such a network might proceed at much slower speed than the bandwidth could offer theoretically.

15 seconds for 500 files seems way too slow. Have you downloaded Etrecheck and can you run it and post its report here using the additional text button below (following instructions provided in Etrecheck?

Yida_Li wrote:

Is this expected behavior, and is there any workaround?

Yes. Don't put 20,000 files into a single folder. This is a problem on any operating system, not just the Mac.

on Windows, opening the same folder is instant, and I can scroll and preview smoothly.

I'm not familiar with Windows. I know I experienced the same problem on Linux computers. I'm sure macOS is many times worse because it is going to try to open all 20,000 files to get a preview of the image.

You can try navigating to this folder and then choosing "Show View Options" from the "View" menu. Turn off "Show icon preview". This may help some, but perhaps not. You might find it recommended elsewhere. I only mention it just to recommend that you don't get your hopes up.

Yida_Li wrote:

So I suspect this is a macOS-specific issue, or perhaps there’s some particular bug in my system.

Yes and no. The important part is that it's your problem to fix. You simply can't have that many files in a single folder. You'll have to organize them somehow.

Yes, in theory, macOS could be "improved" to show 20k files. But how many people can meaningfully scroll through a list of 20k files and find the one they want? The fact that other systems might be able to do it doesn't make any practical difference.

Yida_Li wrote:

Both external drives are formatted as exFAT, which is the most common formats for external storage devices. I would expect both macOS and Windows to have solid support for exFAT, so the file system format should not be the issue.

Mac does support exFat but it might not have the same efficiency with 20,000 files on a Mac. I would try with a separate external drive formatted as APFS. That is not the solution for use with Windows machines of course but it could be useful as a test.

On Windows, opening the same NAS folder or the same external drives is almost instantaneous, and the icons/thumbnails load very quickly. This suggests that neither the NAS nor the drives themselves are causing the slowdown.

Or the NAS is configured in a way that is optimal for Windows but not for MacOS. I am not an expert on NAS.

On the NAS, the situation is even more severe

With your ethernet connection the link to the NAS should be similar in speed as to an external drive. So this is odd and makes me wonder about the NAS setup. I don't know enough about NAS to make additional suggestions.

So at this point, I still suspect that this behavior is specific to Finder.

Except others have reported here that they don't see such delays. If it was specific to Finder we all should be seeing it.

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I suggest you provide the report from Etrecheck. It won't provide info about your NAS setup but will reveal if anything installed is having some unwanted impact.

steve626 wrote:

Yida_Li wrote:

Both external drives are formatted as exFAT, which is the most common formats for external storage devices. I would expect both macOS and Windows to have solid support for exFAT, so the file system format should not be the issue.

Mac does support exFat but it might not have the same efficiency with 20,000 files on a Mac.

I believe that FAT32 and exFAT file system drivers now reside in user space, rather than in system (kernel) space. That could have some theoretical security and stability benefits, but it also means a lot more context switching – context switching that can affect performance.

Yida_Li wrote:

I don’t use the Photos app for view these photos because many images from my Android phones lose their correct metadata after import, which disrupts chronological sorting and would contaminate my current Photos library, and my 200 GB iCloud plan cannot accommodate this entire archive.

Then use some other photo database tool for those. I'm sure there are many.

I’m already using Name List view in Finder, so it shouldn’t be generating any image previews in the first place.

That's not how it works. You have to turn off that specific setting. And even then, I'm not sure if that would turn it off. It may only turn off the display of custom icons.

If I do want previews, I can implement asynchronous, batched thumbnail loading in another 200 lines of code.

Then write your own photo database and sell it!

And no reasonable file browser loads every thumbnail at once.

I never said Finder was reasonable.

I assume Finder is not intended to load all thumbnails at once, as that would be inconsistent with normal software engineering practice. Even if Finder did work that way, loading thumbnails for 20,000 images is not a difficult task on modern

hardware — especially given how fast the M-series CPUs are. It should take no more than one minute, not an hour.

It's not a factor of the CPU. It's a factor of the file system speed. You're using SMB, which is very slow and has no optimizations.

The entire network path between my Mac and the NAS is a wired Ethernet connection, with no Wi-Fi involved anywhere in the chain.

It's 2025. Wifi is usually going to be faster than a wired connection.

Even if Finder were downloading image thumbnails, the bandwidth would still be adequate.

It's not just downloading them. It's generating them. And then it's caching them. And then it reads the cache. And then it reads the attributes. And then it updates the .DS_Store. Take one down, pass it around, 19,999 files to go.

Have you installed and run any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on your Mac?