I recently added a Seagate 400Gb SATA drive to my system, and it has been behaving strangely since I put it in.  for one thing, the BIOS S.M.A.R.T. came up with a warning the last time I booted with it enabled, saying that I should backup my data and replace the disk (!). 

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What is a good program out there that exercises a disk to give some assurance of errors or lack thereof?