This leads me to believe that the volume size is limited to 32GB (Microsoft imposed on their format after W98) instead of the original 2TB, something that you can verify. Limits on some things such as volume and file size are missing from Mackie's specs.
No 32GB limit on the DL32R - I've got a 1 TB hard drive attached, formatted on the DL32R, which works nicely. Currently about 100 GB occupied, so definitely more than 32.
And yes, I haven't found a function to delete individual songs in Master Fader - not much of an issue for me, since I routinely move my tracks to my PC to edit / mix. I also prepare some multichannel wave files on my PC to use for sound checks and move them onto the USB drive - works nicely as long as you don't mess up the file naming convention.
Must admit, I haven't used the disk recording function a lot recently, since direct ASIO recording to REAPER or Tracks Live is far more convenient in the studio / rehearsal room. But for capturing a live gig, the capability to easily record to a USB drive (I use a 250 GB Sandisk SSD drive, so no issues with vibrations on stage) is just great. No need to drag along a recording laptop - simply plug in the drive and don't forget to start the recording...
Cheers,
Torsten