The Mac diskutil command-line tool says "SMART Status: Verified", which isn't terribly believable. Otherwise, there's the "Disk Utility" GUI app, which just fisnihed 'verifying' the disk with the similarly unhelpful message "volume checked". Verifying the boot disk requires some gymnastics with an OS X boot disk, so I'll deal with that later. (What really matters to me, though, is the secondary disk, since that's where my MP3 collection lives...)