I’ve just had both 2TB green WDCWC20EADS drives fail. This looks to be the cause of the flaky it’s critical and now it’s ok behavior I’ve been seeing for the last couple of months or so. The bottom two drives have bad sectors mapped or are taking 20 seconds to respond sometimes.
I came across this thread:
It looks like the green drives or desktop drives in general are not suitable for RAID service because either the cause to many head load cycles OR the way they do deep drive recovery on errors takes too long and causes other problems.