[Jetlag]

A couple of thoughts.

WD lists their 2.5TB drive as having "Non-recoverable read errors per bits read" as "<1 in 10^14" and the drive has about 2 x 10^13 bits, so while the chance of an error in one whole disk read is non-trivial, it's not 100%.

Mirroring will still work fine as long as the error is detected. The chance of read errors in the exact same sector of two disks should still be small. Silent errors were always a problem for mirroring.

At what point do we as consumers start considering drives to be defective? Is the underlying ECC suffering because of the need to hit greater storage numbers?