Hello,
thanks for the info. Lack of support for exFAT in OMV is indeed the problem.
Using extX for the external disk is not an option for me; I've had negative experience with MacFuse under MacOS 10.9, resulting in massive data loss.
I tried to patch OpenMediaVault by adding a class OMVFilesystemBackendExfat.
I managed to get the filesystem backend registered, now the "filesystems" view shows the partition, but when I try to mount it through OMV, nothing happens - no error message or anything, it just doesn't get mounted.
OMV doesn't seem to write any logs, so I don't know what goes wrong.
Of course, I can still mount the partition from the console. So I can select the disk for shared folders etc.
This is my workaround for now.