Thanks - I do concede that SMART data is somewhat unreliable as an indicator. The Areca cli as the OP stated is pretty good in this regard already.
So let me explain my requirement. I've got 89 drives attached to my storage computer - this will grow in time. 24 x 4TB, 24 x 2TB, the rest of them 3 TB drives. Given that volume and the fact that it isn't a 24x7 server at the moment means in my eyes the surface scans are limited value since the time taken to do some will be significant. Maybe I need to look at the file scans more and see what that does - certainly it would be helpful to automatically record what files what was on what drive if one should fail rather than the DIR scrapes I do currently.
What I was hoping that the scanner would read the SMART data and if there was any "significant" change it would kick off a scan - so more targeted. But without the SMART data this isn't going to work