Thousands of people every day experience what at first seems that their external USB or Thunderbolt HD, either 2.5" portable or 3.5" desktop model is dying, is dead, or all hope is lost for it. Good news is that you have roughly a greater than 50-60% chance that your external hard drive is perfectly fine!
The great news at the end of the tunnel of an apparently failed or failing external hard drive.
When checked on another computer, and with no need for spending money on data extraction expertise or software, the very likely case is that your external USB or thunderbolt HD is in fact fine, and merely the card interface, or SATA bridge card has failed or is failing. Keeping a HD dock around handy, or cheaper still a $20 hard drive enclosure or a SATA to USB connector can be a real life saver in getting your drive back to use, when the drive itself is fine, and merely its interface card has gone bad.
The SATA bridge card inside a USB external HD has a very high failure rate in general
Typical SATA bridge cards as seen inside a 3.5" external HD with power input (#1), and 2.5" SATA cards (#3, #4, #5)
What are the realistic odds your HD is perfectly fine?
There are no hard facts whatsoever, especially since so many people discard their assumed “dead/faulty” hard drives, but a good educated conclusion from years of examining and seeing this issue is that for hard drives made since 2010, and not dropped or generally abused, is that a minimum of 50% conservatively are perfectly fine! I personally estimate however that it likely approaches 60%+.
Considering how many external hard drives ‘fail’ (rather the SATA bridge more than half the time) each day, that is a very high number of perfectly fine HD that are tossed!
This is especially common with 3.5” desktop HD that are connected 24/7 with power and see a lot of data transfer. People wrongly conclude that “X” mfg. just made a defective drive, when in fact their 3.5” drives inside the plastic enclosure is 100% fine. I have personally seen well over 200 of these dead SATA cards and additionally seen 3 fail within a one hour span of doing a large data copies.
One of the very reason pros use bare HD as inserted into HD docks is not just the saving of space and the need for endless USB cables, but the elimination of the need for this high failure-rate part.
While the shapes and sizes vary somewhat on SATA bridge cards, they all serve the same purpose and have likewise failure rates
What exactly is the SATA bridge card in your external HD?
In the middle to late of 2009, most all external hard drives both in 2.5” and 3.5” reached the shelves in SATA III. These small SATA cards or "bridges" are used to translate between the hard drives’ interfaces and the enclosures' external ports (USB, Thunderbolt, Firewire). Additionally these small bridges not only transfer power but also of course the data. Unfortunately these SATA bridge cards have a very high failure rate as they are burdened with shuffle power and data.
Literally these little unreliable and fragile cards are the power conduits and the nervous system for all external HD data transfer.
SATA card as found inside a typical USB external hard drive
The assumption that the hard drive is bad when its not!
Countless 1000s of good external hard drives are thrown away each year because the owner thought the HD was bad when it fact it was the SATA bridge card which had failed. This card is removed in a matter of mere second once an external USB HD is cracked open from its plastic casing to reveal the bare HD and the attached SATA card which attaches between the HD and the USB cable.
To complicate this problem, even many computer professionals do not know that there is a very easy solution to the “failing or dead HD” issue since the hard drive itself is very likely just fine. Its astonishing that so many highly educated computer repair persons are unaware of this high-failure part, but this is mostly due to the fact that they do not juggle 100s of hard drives and know that of the iceberg that is a “external hard drive failure”, the mostly unseen majority are not a HD failure at all, but a bridge card failure.
To add to this great misunderstanding is the fact that people assume that "likewise symptoms seen on an external HD are the same as seen on an internal HD, therefore also the external HD must be bad". This is a compositional fallacy of logic. Since internal HD do not have a SATA bridge interface, to conclude similar symptoms "indicate the same failure" is misplaced and incorrect.
This is all not to say that HD do not fail, they do indeed, and I have seen many 100s of dead and failing hard drives. Hard drives even under ideal conditions have a life expectancy of around 4-8 years due to ferromagnetic depolarization from entropy. But of the mountain of symptoms that are seen as “hard drive failures” in comments, posts, and hearsay, half of more of these are not a HD failure at all.
What makes up an external USB HD or Thunderbolt HD?
While modern external HD boxes vary in shape and size somewhat, they're the same inside on almost 100% of them.
Four parts essentially:
1. Your 2.5” or 3.5” hard drive.
2. The plastic or metal box it rests in.
3. The USB cable and also (in the case of the 3.5” external) the power cable and block.
4. The SATA bridge card.
Clear USB HD in its case, with green SATA card at top,...not shown is the USB cable
The USB cables are almost entirely unheard of today to fail, and the box enclosure cannot fail, leaving the good HD you have taken care of and the 50 cent part which juggles both power and data to and from the HD itself, that being the SATA card.
What drives will work for this go-around fix?
Almost any drive 2010 and later, all 3.5” HD mid-2010 and on, and almost all USB 2.5” external hard drives, including firewire, and thunderbolt enclosure encased conventional platter hard drives.
The rare exception is a slimline 7mm thick "slim" external HD in both Toshiba and WD in certain models where the SATA bridge has been incorporated into the HD to save money and production costs.
Much older drives 2009 and earlier will not work for this faulty part work around.
How to extract the 3.5” or 2.5” HD from its enclosure?
Almost 100% of external USB and thunderbolt HD are encased in plastic, some are a bit more complex, refer to online teardown instruction on your specific hard drive. In the case of almost all 2.5” external HD, they are contained within a plastic box held together with plastic tabs around the edge in which a thin bladed screwdriver worked around the edge will liberate these plastic clamshell halves revealing the HD and attached SATA card inside. Unhook all USB and power cables to the external HD.
This SATA card unhooks from the HD as simple as unhooking Lego pieces. No prying is needed or tools just separate them by hand. No harm is done in doing this to your external HD unless you drop same in opening up its casing or apply excess brute force that is unwarranted.
This is what should be considered a beginners to beginners-intermediate operation in extracting the HD. If you feel uncomfortable in doing same, don’t do it, but since your data is likely right within reach, and there is an extremely LOW level of damage possible, opening up a USB external HD is a novice operation to perform.
If you paid a data extraction expert to get your data, he would do the exact same thing as this to extract the HD and first verify that that high-failure-rate SATA card is the likely culprit.
Inside a USB hard drive, containing the HD and SATA card
Safe Handling of the bare hard drive
Once the hard drive has been extracted, do not hold or pinch it top to bottom, and try not to touch the HD circuit board on the bottom, hold and grip the hard drive on the thin edge on either side.
Once powered either by HD dock, or USB do not touch the hard drive and especially not its circuit board.
Never open the bare hard drive itself, ever! The screws which hold its casing in place are very sensitive to their tightness. Though there are countless 1000’s of pictures of the inside hard drive platters online with their read heads and actuator arms, these are for demonstration only of what is on the inside of a hard drive; do not open it up to look inside.
Complicated diagnosis from multiple issues
A very complicating factor, the worst in fact, of diagnosing the SATA bridge card as having failed rather than the hard drive itself is that SATA card failure is almost identical in symptoms to the actual hard drive failure.
A couple distinguishing factors are that when the SATA cards inside the external HD are hooked to another computer they may appear as normal, this typical power variance which is odd is typical of SATA bridge failure. Since these bridges not only transfer power but also of course the data, their failure or failing state can show under multiple symptoms making perfect diagnosis often not possible until the SATA card is removed and eliminated as the likely cause of the failure to read and write to the drive.
In addition to power oddities from the failing SATA card, they will often exhibit signs akin to a failed or failing hard drive, but noticeably of course utterly without any genuine hard drive failure signs such as head clicking, or odd noises from the HD itself.
If the external HD seems dead immediately without any signs of slowly dying, or noises, this is almost always a certain sign of SATA bridge failure in an external HD.
Once your rescued hard drive is removed from the bad SATA card
You have several options, but the purchase of a $20 HD enclosure is one option, another is having a HD dock, however this eliminates the former portability in a 2.5" small HD.
Remember that 3.5” HD require power, which means you need either a HD dock, or a powered SATA card kit as seen at top left in the picture below. 2.5” HD get power from the USB port itself.
Just remember that the serious downside to the low cost external HD enclosures is THEY TOO contain these SATA cards, and what is worse the cheap ones will fail, often, much quicker than the original factory one did! In which case it is recommended you buy a quality HD USB enclosure
Rescue tools to use with your extracted HD for data recovery
Thank You & Peace