I recently tripped over someone complaining that there was no good tool to test external disks for OSX.
As usual, because OSX is a superset of BSD unix, the tools are built right in; a few minutes with apropos and man gets you all you need to accomplish the task.
We simply want to do a raw sequential read of the device, tossing the results, but detecting any failures. Assuming the device is the second drive mounted, enter the terminal and type:
sudo dd if=/dev/disk1 of=/dev/null bs=1m
This serves to do a nondestructive read of the entire physical device. For details on the command type ‘man dd’ into a terminal window or browser search field: man dd
For a more aggressive data destructive write test use Disk Utility’s secure erase features, either against individual partitions or the whole device.
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