whiic wrote: or buy a RAID edition WD that has TLER disabled at factory.

It is the opposite, TLER is required to be enabled for hardware RAID.

Could it be too fast headparking problem that make a WD20EADS disappear from a RAID5 on 9690sa. ?

It become visible again only untill that drive get power-cycled.

I've set them all to TLER 7sec wdidle3 at 4.5min , Should I set them to /d 64min ?