FYI, I had to edit /usr/bin/vzdump to change $lvcreate --size 500m to $lvcreate --size 2000m. My vzdump was failing multiple days in a row on my Plesk jail. It has about 60 domains in it and about 30G used, nothing really out of the ordinary. 500m just wasn't enough and it failed and started spewing filesystem errors after about 50 minutes. It's happy now at 2000m.