Cannot find USB harddrive

I am trying to return to Volumio after a several year absence. I forget what version I was using, (1.x I’m sure) but I just downloaded the newest version and am trying to get my system up and running. I have a 320G USB harddrive from an old laptop. I reformatted it to ext4 and loaded it from my Linux box. It works fine on the Linux box. When I plug it in, the power light comes on and the access light flashes and it loads into File Manager. When I plug it into my Pi2 - either before or after booting Volumio - the power light comes on, but no access flashes and no music in Volumio. Other hardware: Pi2 (~3 yrs old), IQaudIO DAC (same age). I wish I had saved my old SD card as it was working great last time I used it several years ago. Although I cannot be sure without music to play, the rest of the system seems to be working. I did set permissions to “anyone” for all files when plugged into the Linux box, but that didn’t help. Any ideas? Does Pi2 or Volumio require a different format for the USB harddrive?
Any help or suggestions to try greatly appreciated!!