@Joe L.
I was running 1.11 :-( Have downloaded 1.12beta now and will see how I go.
I ran pre... -t /dev/sdc (another drive already precleared by 1.11) and it didn't find a valid signature (see attached image) - I'll obviously have to redo every drive, no problem. As the 6 drives all reported absolutely no problems (1 pass), I might use the -n switch to skip the pre/post reads on those drives.
I'll contact BJP999 re: the drivedb issue, thanks. Many things are in flux at the moment with the new versions of unraid, support for 3TB drives etc.
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On another note ... I know the suggested method for running multiple preclears simultaneously is via screen, but I was just wondering if it wouldn't be easier to have that capability included in UnMenu? Or would it be too dangerous if the interface was too easy? Hmmm.