External hard drives keep failing A couple years ago, I learned my lesson. I had bought a WD My Book Thunderbolt external RAID. I didn't have a backup plan of course; it failed within a year, and I lost everything—this was about a year ago.

I went out and bought two 8TB Seagate Expansion Desktop Drives, one as my main storage, and one for backup. I signed up with Crashplan, a service that would backup my files to it's cloud as well as do the job of backing up to my local external backup drive.

A couple of months ago the backup drive died. Within the same week one of my wife's external drives died. 

I invested in a Synology NAS and set up a RAID 6 to throw all my files onto, with plans to attach a 2nd external drive to back up the NAS—but of course, before I get a chance to back up my main Seagate drive to the NAS, my Mac is telling me it has a problem (unfortunately I didn't write down what it said), that it has been set to read-only, and I need to back it up before it fails completely. 

It feels like this is happening a bit too often to blame on "Well sometimes ya just get a bad one!", and I'm wondering if I am overlooking other factors?

Could it be an electrical issue? My house is about 120 years old, but we had the knob &amp; tube wiring replaced when we moved in and a new breaker box installed. All my computer hardware is plugged into a couple surge protectors which are in turn plugged into a UPS batter backup/surge protector. 

Could there be a problem with my computer, doing something to the hard drives to mess them up?

Am I just overusing or overfilling the drives? My work is in graphic design, photography, and video editing, so I'm typically working with some big files, lots of caches, etc. Also I know when Crashplan was backing up to that one external it was telling me it was nearly full. Perhaps I need to be running First Aid on the drives, or rebuilding the directories with Diskwarrior on a regular basis?
It feels like this is happening a bit too often to blame on "Well
  sometimes ya just get a bad one!", and I'm wondering if I am
  overlooking other factors?


Yes!

Based on what you're doing, your using your drives not as a typical home user but more of a "pro" and you should be getting the hardware to match.  Most consumer (especially the entry level drives) have lower MTBF (Mean Time Between Failures) numbers - higher is better - than their "workstation" or "NAS class" drives.  The higher end models also have longer warranties - typically 3 to 5 years.

There are some additional factors you may wish to consider:


Seagate drives are notoriously unreliable.  WD drives are better, but the really reliable ones are made by HGST.
Look to get a Thunderbolt enclosure, rather than a "consumer grade" USB drives.
Populate your Synology with NAS rated drives.  They are designed to run longer, cooler with greater reliability.



  Could it be an electrical issue? ... All my computer hardware is
  plugged into a couple surge protectors which are in turn plugged into
  a UPS batter backup/surge protector.


A battery backup is also a surge suppressor/protector so daisy-chaining one to the next is not a good idea - you could be creating issues if/when there are surges.  If you must add ports to your battery backup, use a power strip, not a surge protector.

Your Backup Strategy

It sounds like you're off to a good start with your backup strategy.  Here's a few points to consider:


Having RAID is good, but don't depend on it for backup.  RAID is designed to maximize data availability (up time), not be a backup. 
The two USB drives attached to the RAID is a good idea.  However, you should be alternating backups between the two.  One for "odd" days and the other for "even".  This will require you to have to different backup jobs but it ensures your data is backed up to two different locations.  Also, to ensure you don't backup corrupted data....


Don't backup the backup!
Backup the actual data only!

Adding Crashplan is also an excellent idea.  Having this backup your files to an offsite location is a very smart thing to do.  Having a regimented backup workflow will ensure your access to data even if your NAS and both backup drives are inaccessible.