I registered here just to reply and say this thread is full of nonsense. Telling everyone to avoid a Seagate disk because of a few people's issues is just ridiculous.
For reference, I have 9 (nine) of these 5TB Disks, bought in the USA in Seagate Backup Plus units. I had 4 of these running externally for a while (4-5 months) - connected to a Mac mini 2012 running SoftRAID 4 - two sets of RAID 1 over USB 3.0. No issues. (since upgraded to Thunderbolt enclosure)
I have 2 running now for about a month, connected to an Asus Sabertooth Z87 motherboard. No issues - 180MB/s read/write or thereabouts.
I have 2 running a simple RAID 1 over Thunderbolt connected to my Mac mini 2012.
I also now my original 4 of them in an OCZ Thunderbay 4 enclosure - running RAID 5 over Thunderbolt connected to my Mac mini 2012.
And then I have a spare 5TB just in case I have a failure.
Again, NO issues with any of these drives. The only thing I had to was run the Mac HDAPM tool to prevent the head-parking issue that OS X is infamous for, but I had no performance issues prior to running the tool, and only did so because I didn't like the noise the head-parking sound made when running media in a quiet movie room. I did the same thing with my older 2TB Western Digital drives, too, so this is not unique to the Seagates.
So again, to the OP, your experience is certainly not everyone's, and telling EVERYONE to avoid Seagate 5TB Externals is just madness.
PS I have several friends with ~15 5TB Seagate drives between them, and neither of them has any issues, either.