Everything? to know about external HDD and Drive Docks.(not  SSD)          
A.k.a  Rust drives and spinners
The word "hard" means hard platter and not old floppy flex media.

We use these devices and product below to test HDD under suspension or to back up data. (any)
The time to backup is before your main boot drive gets corrupted ! (or goes BAD)
I use TODO backup (free) to backup all my data or to clone any drive you want. (It works very good, even to recover just one file later, not all at once!) URL link to TODO.
The external DOCK, or enclosure, or a DOCKING STATION ,  just get this and do not read why it works below, complexity is never simple with computers. ok?
Do know that some folks avoid all this and use cloud storage. (I use private servers local and remote to back up my data and use DOCK's)

This page below is not about turn key, USB backup pocket drives or Backup Plus(tm) type drives already fitted to a tiny case (that mostly just work ok on modern PCs, but not the 100mA version below:
My page is about all PCs working with  the best external drive enclosure or interface or dock, you can make one your self. ( or DIY  and buy the case, then buy any drive)
Rule #1 is for Hard disk drive enclosure limits   is power and current. ( there are 4 levels of current in the spec., but SPINUP current (or peak) is what matters)
The SSD drive has no motor nor any platter nor head servo's to fail so is never a problem.
There are many docking stations, SATA to USB or to eSATA or SATA.
Your PC USB port may  not have enough power to run any HDD   many old PCs have only 100mA of power on the old lame USB ports and can not run vast classes of HDD.
HDD external can need 200mA to 2 full amps(2000mA) and must not be short changed there. (if you do use my dock below there is no problem here)
If the motor in the external drive is silent the power is NO GOOD !
 
The bigger (mass) and more platters and faster the HDD spins (RPM) , the higher the startup current will be  and can fail; (some very tiny and special HDD 2.5" designed just for the bundled enclosure can be max 300mA rated)
To be sure I read the HDD data sheet at Seagate (I am a 100% fan boy of Seagate since they went in to business 1978 and Alan Shugart) and the ST506 (1980)
Read the Datasheet first,  if you want to DIY your own external enclosures.
Some small 2.5" drives are in fact 5vdc only drives and are 200mA motors inside. Again read the spec.s
A good external HDD enclosure like mine runs any drive I want, even power hog 3.5" 10k drives seen here.
The best enclusures made have  2amp or more power pack attached, this is a hard cold fact, not to ignore.
Examples:
The Mobile  ST2000LM007 2TB 2.5" new +5v only drive uses only 1amp to start the motor.    (see many specs here look for "SpinUp" current a single word)
My 3.5" 2TB  enterprize HDD use more power. ST3000DM001 2.0amp (12v) spinup current , others  ST31500341as  go as high at 2.8 amps.
 This newer modern 2.5: Seagate hdd  model , 2TB sizes, ST2000LM007 , run on 5vdc only and needs only 1amp to start the motor, and 0.1 amps idle, and 0.36amp  running average.
Even the moblile 5400 RPM  Seagate Momentus 5400.6 ST9500325AS , needs 1 full amp to startup and 2.85watts to run.(R/W)
I will not cover the non-sata HDD, I call them USB direct, and have no actual SATA ports real.  as seen here, WD passport  WD20NMVW.
 (the  VW means a queer drive, non SATA, but uUSB) WD  and Seagate treats these cheap HDD as toys and have no real datasheets at all, but I took them apart and found near real 2.5' HDD inside and  real datasheet and startup is 1.1Amps.! I can tell you for a fact my PCs can not do that on any USB port.
The fast cures is in my list at the end of this document, the below the how  and why in details .
USB hell: (cured using my special USB enclosure)
Vast models of PC can not ever do USB power  demands 100MA to 2amps. (only USB -C can do 2amps)
I have USB current tester and tells me in seconds what power is there,  at full load 4.6vdc minium voltage drop (from 5v) and  the current it can handle.
The wiki is some help here. See this chart, see 100mA hopeless ports?  Many External drives run fine with USB v3.  900mA is concidered minimun on most modern PC. USB -C tops the cake, at full 3amps 15watts.
USB-C can run any drive made.

Wiki made chart,  Go USB3 at least. end topic.
The cure is simple use only Enclosures and DOCK's with its own power pack rated 2amps or more. (SOLVED)! or buy the BC1.2  powered hub with a 5amp power pack!
DIY:
  The   Choices to pick when buying a dock. (I wll all any enclosure external a dock now)
  1. Form factors, A full enclosure, 2.5" or 3.5? or even both , a docking station box and last just  cable adapter for just cloning or just erasing (DBAN) drives.
  2. A Dock that has USB port and cable  eSATA: (both be nice)
  3. A 12vdc power pack rated at at least 2.0Amps or more that comes with the DOCK kit.  ( 1amp to 3 amps current can flow at spinup)
  4. Fan in the box is good for any hot running HDD , as seen with 15,000 RPM HDD Cheetah 15K.7  some fast drives run hot.
The goal is to get the HDD motor spun  up fast and not let that delay or the HDD can get confused or even crash the heads trying and failing to reach spec,RPM 7200 is common speeds now.
I call this getting over the SPINUP HUMP:   All PCs and for sure gutless USB or any bad enclosure (dock) will fail if power (amps)  is not at 2.5amps,  the motor will fail to reach full RPM and the drive errors out.(or loops madly)

This is scope view of current (using a current probe here)

The docking station must provide full power at all times to the HDD,  using an external power pack
The exception to this is , many turn key data storage devices, use USB port and do work (some don't) but the new ones all do with 1 amp or far less.
The below trucj ub Device monitor allows me to see spec power and actual ("required"  96 is an average only.
 Motor spins up,  (RPM and platter mass sets current needs)
 
My fancy external drive, 2TB and one 3TB runs 100% perfect at 2amps, now for 10 years, 2009 to today.  with SEAGATE drive inside, 3.5"
See that power jack do not forget to use power and end all problems now.  (2Amps or more)

This is one of  my drive cases, it also uses eSATA,  cables. (and is much faster than USB2)
The Case comes new with  large power pack, USE IT AND WIN. the startup battle.
 In fact this Case above runs on ANY PC made no issues at all. (over 20 tried , Dell, HP, PCs laptops ,servers all work) Because it is SELF POWERED properly.

Learning point 1:
Old Laptops with 100mA ports will not like to run an HDD directly and charge cell phone battery at the same time, or run 250mA lighted Corsair K55 or K70 keyboard either at the same time.

 HACK1: (this can work or not,  it is a marginal solution to this problem)
One can increase USB power by 2 times with this cable.

I know for a fact these cables can work, but for a fact it will on work on all HDD made, after all many HDD will not startup with  1 amp. of current. (a fact)
Trick #1,  kee the 2 reight ends below on widely spaced USB ports.
The silly USB  ports on dirt chip Laptops can be  shared ports ! if you overload one port you find out 2 or more go offline. (fun no?)
If the 2 ports you picked are in fact shared (an OEM freak'n secret) it will fail still.
This love to fail because 4-6 ports on any PC are shared, so no current gains (Amps) possible.  SO IS USELESS. (unless you know how your Vbus is wired in your PC)
This hack below can work  but be sure not to pick 2 shared DC ports (means VBus power is shared 5vdc) or is useless as can be.
If each port is 500mA rated now you have 1amp to start up the motor. 

My hard drive external failure list: (dead)  (bad drive, dead USB port, bad cables, wrong cables , wrong power pack)
  • Plug in the dock and power to the dock and USB to the USB port, Turn it on and hear the motor spin up.
  • You put your  ear to the HDD case side, and hear the motor start , it sounds like very tiny jet engine spooling up.
  • If the HDD clicks like mad or is dead slient the HDD is bad or has no power, or power is crazy weak.
  No POWER NO JOY  !
ONE MORE POWER GRAPH (SCOPE VIEWED LIVE
The External HDD is:  The drive maker seagate used Ocillicope and a nice current probe to do this, (means it's REAL)
 
Seagates current 3.5" "Desktop HDD series" (runs 2 to 2.5AMP startup in red below, on the  12vdc line.
This current is huge, and power on 2.5inch  is 5watts max but this one is 30watts,  6 times more.!!! 6 Time more power is needed to spin up this large HDD.

This is an Enterprise drive:
The green line is 5vdc turning on .(the step)
 The red line is 12vd motor startup current on the  ST6000NM0235 drive.
Again these are scope views with current probe on the motor power wire. 2.52 Amps to start up motor (in red)
I hate to tell you USB can not run this drive for POWER. Unless TYPE C or better. (charger current rated USB ports may work here, I have not tried it)

This Drive run great in my powered external case and my DOCK USB and eSTAT both work.

If power is lacking you will hear the HDD try to spin up then fail and spin down , repeats forever and is not good to run any drive like that for more than a minute or 2.
eSATA: (cable connected HDD) (some PC can even hot swap the cable setup correctly)
Some laptops do not have a 12vdc pin on the eSATA port,  making the motor dead, on any connected HDD. (unless you connect a 12vdc power pack to the drive.)

I use only 3.5" drives for  backup and are enterprise grade, and 2TB or larger. (I also have backup servers at home and on the www )
This  Enterprise HDD  have longer life spans of + 10 years, unlike toy grade used, laptops 2.5" drives that have 1/2 the life span of good drives. (real SAS drives even better)

MY RECOMENDATIONS: (for Case/enclosure boxes)  I like dual sized drives and only with a full 2amp power pack or larger amps. USB3, works for cloning or backup duty)
MY BEST DOCK: Love this docking bay. Runs any drive made connected to any PC you can dream up old or new, does them all. HDD and SSD any size.
Love it.
One more my fast and high powered, enclosure below. (seen this on ebay.com)

ORICO 3.5 inch USB C Hard Drive Enclosure for SATA HDD Support Max 8TB UASP SATA

Runs my  TB-3.5" HDD 6TB at full speeds,  200MB/s  in fact more. Nothing faster exists for fastest 6TB HDD on earth.
I have the fastest HDD on earth in the box. From MIGHTY SEAGATE !  WD can go fish.   Costs more but IS MORE.
with 12vdc 2.0amp power pack. (read speed in the image are wrong, they have a slow HDD)

 
Solutions to a dead or flaky HDD external recap'd: Lightning fast cure list:
  • Use only USB BC1.2 high current rated cables only!
  • DIY  case , buy it and get 2 or more AMP power pack with it,  (2+amps for 2.5" or 3+ amps for 3.5" inch) see my trick there make inches = amps, or more. easy no?
  • Buy  A real powered hub with the great VIA  VL812 chip inside.
  • Buy a USB 3,  BC1.2, rated PCI-express USB card. bingo 1 step done. (newegg.com sells them )
  • Buy a SSD drive external, but over 1TB go broke fast.  or see my Docking BAY above. (or the Orico)
  • Build a file server, (endless options) but yah not vary portable, sure.
Once connected you can :
  • Drag and drop 1000's of file to the drive.
  • backup mp3 sounds or MP4 videos here.
  • you can run backup software of vast kinds and backup to here. like TODO backup (free)

version 5  8-8-2017   (7-7-2020 revised)