backup of system data volume will not mount
 

I have an external drive partitioned into two APFS volumes (but only 1 container). I ran SuperDuper! to clone my laptop Catalina (10.15.7) system drive to one of the partitions on the external drive.

SD seemed to whirr away just fine, and terminated normally. I watched it while it was working, and both the system and data portions of the laptop boot volume seemed to be copied, and the SD log seems to confirm this. BUT, only the system volume and the existing other volume mount on my desktop; the system data volume does NOT mount.

I'm attaching screenshots of my desktop showing only two volumes, and also a screenshot of Disk Utility, which clearly shows that there are 3 volumes on the target drive, AND that the target system data volume is mounted. In case it is helpful, I'm also attaching the SD log file from the copy job.

I did try rebooting, which didn't change things. I also unmounted the target system data volume in Disk Utility and mounted it again, but it still didn't appear on my desktop. It also doesn't appear in a Finder window if I go to the topmost level.

If I do a ls /volumes command in terminal, I see the volume, so it's obviously there. So why doesn't it show up on the desktop or in Finder?

Folks - it's a bad idea to post this kind of thing in the forum. There's a "Send to shirt pocket" Button in the log window for a reason! It keeps your log information in a private, rather than a public, space.

Anyway, it doesn't show up because that's how Finder works. You can get to it either through the system volume (via its firmlinks) or by using Go To Folder to open /Volumes, and you'll see it there...

I was trying to make things easier for you so you wouldn't have to associate a forum post with attached screenshots with a log file that came in separately...I won't do it again. Sorry.

Yeah, I know that's how Finder works with Catalina system volumes, but what fooled me was that when I did a Get Info on the volume name after the SD copy, Finder reported only 11GB on the drive, which I figured had to be the size of the system, not system data, volume. After reading your response, I rebooted the laptop, and then Finder reported 200+GB, which is what I would have expected. Must have been a temporary Finder glitch.


Followup question about partitioning an SD target volume in a system backup and another volume. I did it so that both partitions were children of the same APFS container. I know that one can also create separate containers, but those will be fixed size, of course. Is there any reason to prefer one approach over the other?

The only reason to hard partition a drive is to separate the containers, something that's really not necessary. The only upside I can think of is that container corruption could affect more than one volume - but I'd probably rely on redundant devices for protection there, rather than separate partitions.