By accident I just noticed that when I resilvered from a disc reporting pending sectors to another used disc, that after resilvering also reported bad sectors and I changed to a second disc and resilvered again. The first one took some nine hours to resilver and the other one just some 3-4 hrs. The first was a 7200 rpm 1,5 Tb and the second a 5400 rpm 2 Tb. It feels like the data must have been more favorable structured the second time. The rig is a 10 disc Z2.