These are SAS drives connected directly to a RAID controller on each blade, so a chassis backplane issue is unlikely.

There is a known issue (though not with this drive model) where high throughput can break a mirror, presumably due to timing issues. However, these drives fail when the blades are near idle.

I've just received a drive firmware update - transferred via a third party file hosting site as this major player could not mail or FTP host the 9MB file!?

We'll see if it helps...