Time Machine backup failure
My 2012 27 inch iMac running Sierra with a 3TB fusion drive has worked flawlessly for 8 years, but now the time machine backup fails (worked with same disk since September) then suddenly stopped- it copies for about 15 minutes and then fails. The disk seems to be ok, and there are backup files on it. I bought a new 4TB disk, and it also fails in the same way. From searching online it seems this can occur and the solution i found was to give up and use SuperDuper!. Does anyone know how to get timemachine to work again?
thanks,
JP