Catalina 10.15 and external hard drive issues

On a 2019 16" MBP, running 10.15.2 (19C57), I'm having similar issues.

a) I removed a 2 TB SSD I got from Crucial/Micron a few years ago (MX300) from a 2012 MBP. I installed the drive into a Cable Matters enclosure with a USB 3.1 Gen 2 interface. The drive has about 1 TB of data on it.

b) I'm using a USB-C to USB-C cable to connect it to the 16" MBP.

c) Leaving the 16" computer connected to power and set to not go to sleep (except the display), I let Spotlight run overnight, so it could index the external drive on the new computer. It seems to have worked fine.

d) Today, I've been copying large numbers of files from the external SSD to the internal SSD of the new computer. Finder searches seem to work OK. Copying and pasting went fine for awhile. When I got to working with images, though, the drive (or connection, or something) started making the Finder unresponsive.

e) I have about 50,000 images on the external drive. I was hoping to be able to exclude the Pictures folder on the external drive when searching for images (since iCloud had already copied my Apple photos to the new computer), but I'm not sure that the Finder allows one to exclude a particular folder from a search. Anyway, I narrowed the list of interesting images by only searching for image files greater than 900 KB in file size. That got me down to about 5000 images.

f) At first I tried selecting all those files and copying them to the clipboard. This resulted in the Finder becoming unresponsive and eventually the external drive was ejected (by some process, not by me). I wondered if maybe I had selected so many images that I ran out of of RAM in the copy process. I rebooted and started over.

g) This time I copied about 500 files (~ 7 GB) to the clipboard and then to the internal drive. That went fine. Then I selected the next ~ 700 files (~ 31 GB) and copied them to the clipboard. That group also copied to the internal drive. When I selected the next group, the Finder again became unresponsive and I had to relaunch it. It took what seemed to me like a long time to relaunch (~ 30 seconds or more). Over the next few tries, I had to relaunch the Finder multiple times. Sometimes the external drive would remount and sometimes it wouldn't. (Even if Disk Utility could "see" the external drive, it might not mount it.)

h) Now, I seem to be able to replicate this problem (that is, make the Finder unresponsive) just by browsing certain files on the external drive. For instance, some of the images on the external drive are named "CCAPxxx.tif" and/or "CCAPxxx.png". If I skip past these files in the Finder search results window, the Finder continues to work. However, if those files are visible in the Finder search results window (or maybe if one of them is selected), the Finder becomes unresponsive and needs to be relaunched, and the external drive will likely be disconnected in the process.

Thanks for reading.

Revert your Mac to a previous macOS version - Apple

Are you using the software that came with the WD drives? If so uninstall it as it's not needed and can interfere with the macOS drive management function.

It's a bit late now but for future EHDs consider either convential OWC Mercury Elite Pro external HDs or Mercury Electra 6G SSD external HDs.

Several important points have been made that I just want to repeat:

1. many drives come with software that offer certain services. I've never found any of that third party software helpful. To the contrary, in many cases I've seen it cause trouble. Don't use it. This can especially be an issue at this time of the year - when Apple has just released a new OS. Driver level software is often broken by OS upgrades, not to mention security updates.
2. Mojave's Disk Utility may be more trustworthy at the moment than Catalina's. This is one of the many reasons I have both a Catalina installation (internal drive) and a Mojave installation (external drive) and I'll keep the Mojave installation at least until September next year.
3. external drives found at big box discount stores are often of doubtful quality. While I can recommend Western Digital bare drives, I never recommend their externals. I trust my media files and backups to OWC drives enclosures and I build my own drives.

Firstly unplug your hard drives. Catalina has blown up 2 of mine. Both WD 4T drives are ruined, that’s my TM for over 5 years and my iTunes. I was nearly sick. WD just said they aren’t supporting Catalina yet. Nothing could be done. In new caddies now and working but everything lost. Apple don’t mention this. Had to wipe the Hard Drive on my new iMac and reinstall Mojave to get stuff working again. Catalina = Vista

This is not a problem of the disk itself, but a mounting problem in the system. I have the very same problem with my SMB shares. I can mount them after a boot, but when I close my Mac, instead of disconnecting as they would normally do, finder shows the disks are disconnected, mounting point folders remain at the same place, but all are renamed to "OS X" (but on desktop the names remain the same) and I cannot get rid of them. But that does not matter, because running my AppleScript with "mount volume" command does not work anyway. The app gets stalled. This is obviously a bug and I hope it gets fixed soon.

Oh and by the way, after this happens, I cannot restart normally, but often have to force it. Also if I try to mount the volumes too soon (when not yet correctly connected to network for example), the mounting gets stalled and I have to do another restart!!! My Mac is virtually crippled right now.

As I said, it broke both of my WD 4T Mac OS Extended (Journaled) drives by crashing and restarting so much. WD said it's nothing to do with them. Had to completely wipe my hard drive, with no Time Machine or clone because the drives wouldn't work and reinstalled Mojave. Moved one of the drives to a new caddy but still unrecognisable by this machine. So had to reformat if, that was after extensive data recovery software getting nowhere. Catalina = VISTA

I'm chiming in to say that I am encountering the same issues. I have two Seagate external drives that work perfectly on Windows and on my older MacBook Pro, which has High Sierra installed. I got a new 2019 MacBook Pro with Catalina 10.15.3, and when I plug in those same Seagate drives, they do not mount. I am able to see that they are "visible" to the computer by navigating to Utilities -> System Information, but that is as far as it goes. I don't want to mess around with the hard drives, as they are still actively working on the PCs.

It is completely unacceptable that this post was made in October 2019, and four months later, there are still no fixes. I suppose my next step will be to buy new hard drives that purportedly work on both Catalina and PC and then copy all of the data from my older hard drives to my new ones. I'm very unhappy that I have to drop hundreds more dollars and several more hours to accommodate my absurdly expensive new MacBook Pro.

I agree mate.

It destroyed my 2x 4TB Western Digital drives, they wouldn't mount. I purchased 2 cheap enclosures and swopped out the drives.

The drives were unreadable.

Reformatted and working fine now BUT lost all data.

WD said nothing to do with us! One would have thought that they would have tested their Mac 'My Cloud ' drives with the beta OS and figured out something needed doing!

Wont be using them again.

I 'd try to use ONLY Mojave's Disk Utility currently. I don't trust Catalina's yet.

I've bricked two Seagate external drives within 24 hours of putting a Catalina Time Machine backup onto them.

I too have similar issues.

Thought I'd share that what is dead under Catalina is alive & well when I connect to my wife's newer Macbook Pro but running under the old system.

Hope it helps.

This is my story too.

It took me sometime before I suspected the problem with the upgrade to Catalina.

I searched online for a solution, but it seems this is the best place I found useful information about what happened. I have all my data in my external and no backup. All data lost? Is there any solution for all?

Yep, I am having the same issue. My workflow has been to store and edit photos on an external drive (both a 4T hard drive and a 1 T SSD). Since upgrading to Catalina, this is now longer a trustworthy process. Photoshop and Lightroom both lock up, and a problem with Finder will not allow me to eject the drive or even restart the computer properly. Finder ends up locked up, unable to restart, with my MacBook Pro's fan spinning full blast.

Fortunately my SSD has remounted each time I have done a hard shut down with the power button. I can't say the same for my 4T drive, which is currently at a data recovery establishment. I am not at all impressed with Catalina.