system
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Yes, they were bought as a matched pair.All still seems quite stable at the moment, so I’ve just ordered a 250GB Samsung SSD. They seem to be the most reliable ones as far as I can tell.
A job for after the holiday I think though 
The offending drive, whilst it was loaded with the RAID drivers ,is actually one of the motherboard drivers anyway, so would have been loaded regardless.
Thanls for your assistance and ideas, back to planning the holiday for a while now.