opening photos Library stored on WD external hard drive

There are other things that may cause the Mac to be upset with the drive. Here are the first things I think of: Exactly how is it formatted?  To get full functionality (and to avoid damaging the Photos Library) an external drive must be formatted in either APFS format or Mac OS Extended (Journaled) format. Additionally, the drive can not have had Time Machine on it since it was formatted.

Move your Photos library to save space on your Mac - Apple Support

Make sure that the “Ignore ownership on this volume” checkbox is selected in the command-i info window for the drive. I wouldn't pay attention to what the WD people say about downgrading!

You can use the Disk Utilities app to see details about the formatting and status of the drive.

Yer_Man wrote:

thank you, it is formatted MacOS Extended and ignore ownership is clicked. May have to just move all the (unorganized) photos into Mac HD and recreate the Library. At least all the images are still intact and we still have iCloud back up of images

Create a folder on the drive. Move the library into it. Then try open it.

May have to just move all the (unorganized) photos into Mac HD and recreate the Library.

Why? Why not just copy the library - unless you're running a referenced library. You're not are you?

Right! Or just try to drag the library to your internal drive and see if it works.

If you've check "copy" in Photos>Settings, then it's not a Referenced Library--that's good:

This is the default status.

The error message you are quoting is saying "The library is on a Read Only Volume". Photos needs Read/Write access to the library, even if you just want to browse the library.

As far as I can tell, you can get this error message, for two possible reasons:

• If you are having any backup software installed on the external drive. Is there any software installed on the WD drive for automatic backups? In that case it might help to remove the installed software. Any kind of automatic backup software on the drive can interfere with the file ownerships. Then the "Ignore ownership " flag will not help
• What kind of USB connection does your drive have? A very new Mac, like my current MacBook Air, may only have USB 4 or USB 3.1 gen 2 ports. Since macOS 14.2 I can no longer open the Photos Libraries on my older drives with USB 3 gen 1 ports, even if the MBA is mounting them. I can only access them on my older Macs with macOS 10.14 Mojave and are in the process to copy all libraries from the drives with USB 3 gen 1 ports to a new drive with USB 4 ports. On a new drive with USB 4 IUSB 3.1 gen 2 am no longer seeing the error message "read only" when I try to open a Photos Library. Unfortunately the USB 4 drives are rather expensive, but much faster than the USB 3 models.

thank you, it is formatted MacOS Extended and ignore ownership is clicked. May have to just move all the (unorganized) photos into Mac HD and recreate the Library. At least all the images are still intact and we still have iCloud back up of images

Create a folder on the drive. Move the library into it. Then try open it.

May have to just move all the (unorganized) photos into Mac HD and recreate the Library.

Why? Why not just copy the library - unless you're running a referenced library. You're not are you?

"spent many hours organizing Photos Library (year, month, event etc)"

First, I assume you did this via the program interface and did not muck around inside the library.

Second, "event" is an iPhoto thing. Is this an iPhoto Library being opened on a very new computer with Photos?

Are you running a Managed or a Referenced Library?

A Managed Library, is the default setting, and Photos copies files into the Photos  Library when Importing. The files are then stored within the Library package

A Referenced Library is when Photos is NOT copying the files into the Photos Library when importing because you made a change at Photo -> Preferences -> General. (You unchecked the option to copy files into the Library on import) The files are then stored where ever you put them and not in the Library package. In this scenario you are responsible for the File Management.