I'm posting here before going through all the fun to do up a real bug report to see if anyone else has seen this behavior.
I have two identical Dynex external USB3 drive enclosures with identical 3TB drives in each enclosure. The dmesg output shows: $ dmesg |grep TOSHIBA [ 59.942546] scsi 7:0:0:0: Direct-Access TOSHIBA DT01ACA300 PQ: 0 ANSI: 6 [ 86.301123] scsi 8:0:0:0: Direct-Access TOSHIBA DT01ACA300 PQ: 0 ANSI: 6 $
HOWEVER, the 'Disks' utility program only sees the first one plugged-in, and not the second one. It doesn't matter which one I plug in first; the second one won't get seen by Disks nor will it get automounted. It doesn't even do the 'USB device inserted' sound, for that matter. As another oddity, one of the drives has a LUKS-encrypted ext4 filesystem; the other has an XFS filesystem; if I plug in the XFS-formatted drive first, the LUKS-encrypted on will no longer automount even if the XFS-formatted drive is unmounted and unplugged first, but the the converse does work (mount LUKS+ext4; unmount and unplug; plug in XFS, it gets automounted).
If I plug in the LUKS+ext4 disk first, enter the passphrase, and let it mount, then plug in the XFS drive, I can then manually (from the command line) mount it just fine and both drives work just fine. Both drives work fine when used singly, but not when both are plugged-in.
So, has anyone else seen this? I don't mind filing a bug report, but I am at a bit of a loss as to what component to file it under. I haven't dug into too many logs or other files as yet, but I can if I need to do so. I ran into this making an encrypted copy of the contents of the XFS disk, which will be wiped and reformated LUKS+ext4, and I'd like to make these two drives back each other up.
If I plug in a different USB3 drive, such as my 4TB Seagate, everything works as expected; it seems to only be the identical drives that confuse whatever process is detecting this.