I have a Seagate Backup Plus Slim 1TB external hard disk drive that I'm using to store a lot of large files. I have files from both Mac and Windows (as I use Parallels). I was trying to create a new iPhoto library on my eHDD when it started to give me an error. I think that iPhotos requires Mac Extended (journaled) or maybe exFAT format for a library to be written to that volume but I'm not sure. Even if I did, would my windows files work without any issues on Mac Extended? Is there any way to create an iPhotos library on my eHDD hopefully without formatting it?
You can create a second NTFS partition on your windows machine, then reformat the new partition on your mac as Extended journaled as per Apple specs.
In mac operating system , you need to use the extension as Mac OS Extended, Journaled format as per the apple policy, to access the files to the Mac apps. But you can use some third party apps in windows to access the Mac OS Extended, Journaled format . Third party app like paragon . Which is paid you can find the crack one. So you can you use it in both windows and mac. Hope it helps.
Both iPhotos and Photos require a HFS+ partition. I recommend you go into Disk Utility, shrink your current partition, and add a new HFS+ partition where the free space is.