External hard drive deep freezing Macs
I had this same issue, when I backup a Laptop from OSX to my External HD.  Months later, I was taking the backup HD, and cloning it's content to a Sparse file via SuperDuper.  However, randomly the process would die and the HD would act like it locked up.

For me the solution was to stop Spotlight from Scanning the HD.  This allowed me to utilize SuperDuper again, to take the image from the HD, move it to a Sparse image, which I could then backup on a NAS or offside disaster recovery, freeing the HD for other jobs.  I included the steps from an [article that helped me] to avoid future dead links.

Exclude Specific Items from Spotlight Indexing


  This is by far the simplest way to universally exclude something from
  Spotlight searches and it works in all versions of Mac OS X



System Preferences from the  Apple menu and choose the “Spotlight” preference panel
Click on the “Privacy” tab
Drag &amp; drop folders or drives to exclude from the Spotlight index, or click the “+” plus icon in the corner to manually select hard drives or directories


Result:


  Spotlight will now NOT scan your HD, thus it won't hit that corrupted
  file or OSX unfriendly file.