one of two ext. hdd not showing

April 14, 2012 at 13:05:37
Specs: Windows 64
I have three external hdd, two of which are identical. My laptop (win 7 64x) will only see one of the two identical at a time, even though they have different drive letters. I have to plug / unplug one at a time, and is driving me mad. Help pls.

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#1
April 14, 2012 at 14:34:24
Are these the notebook type external hard drives? If they are, this means that you are pulling too much amperage through your USB ports and the voltage is dropping in such a way that there is not enough power to spin all the drives.

You should purchase a powered USB hub, one that plugs into the wall.


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#2
April 14, 2012 at 19:43:19
Whenever you intend to unplug an external hard drive (or a USB flash drive, or a memory card) while Windows is running, you MUST click on the Safely Remove Hardware icon in your Taskbar at the bottom right of your main desktop screen, and choose to STOP accessing the drive letter for it BEFORE you unplug it, otherwise you can DAMAGE the data on the device.
The icon may be hidden. If you don't see it, click icon the arrowhead at the left end of your icons there to reveal it.
...........

External hard drives require that the USB port you plug them into is actually able to supply the max 500 ma of current (amperage) each.

A USB device may NOT be detected properly when it's plugged into a port in an external USB hub, even if the hub is "powered" (has it's own power supply).

External hard drive requirements in this....

Troubleshooting USB device problems including for flash drives, external drives, external memory card readers.
See Response 1:
http://www.computing.net/answers/ha...

For some desktop mboards you can have problems when an external hard drive is plugged into one of a pair of USB ports on the back of the case that are connected to the same USB controller, if there is another device plugged into the other USB port for the pair, because the pair can't actually supply 500 ma per port - they can only supply 500 ma in total. Usually those pairs of ports are one above the other, not beside each other. If you have two devices plugged into such a pair of ports, try plugging one of them in elsewhere on the back of the computer.

For MANY laptop and netbook mboards similar applies. The built in USB ports often cannot actually supply 500 ma per port - they supply 500 ma in total for two ports that are close to each other. In that case, the external drive should work fine if it's the only thing plugged into the USB ports built into the laptop or netbook, or if you have more than two ports, the only thing plugged into two ports close to each other.

If you want to be able to have more external hard drives recognized at the same time by your laptop, you may need to buy yourself a PCMCIA (PC CARD) or ExpressCard USB 2.0 controller adapter and plug one external hard drive into that.


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#3
April 15, 2012 at 05:47:19
Just for a heads up, most external 2.5" drives pull anywhere from 700ma to 1000ma so they exceed the USB standard of 500ma from the factory already.

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Related Solutions

#4
April 16, 2012 at 14:10:56
The hard drive enclosure may show you that it isn't getting enough current from the USB ports you have it plugged into.

E.g. I have one older external 3.5" drive that requires a power adapter to be plugged into it, two external 2.5" drives in Vantec enclosures, and I used to have another 2.5" drive in another brand's enclosure.
When they aren't getting enough current from the USB connection......
- one of the leds on the drive blinks that is normally continuously on when the drive is getting enough current
- or - one of the leds on the drive that can be two colors is the error color - e.g. red rather than blue or yellow.
.....

I looked up the specs of, and info about, current new 2.5" hard drives about three years ago when a couple of friends of mine wanted to know if they could install a larger capacity drive in their laptops - those laptops are about 6 and 7 years old now (no bios restriction regarding the max capacity that could be recognized).

What I found at that time was that ANY size of current 2.5" drive could be installed in those laptops because there was NO problem regarding that for current 2.5" drives, and for drive models up to, say, 3 years older.

There WAS a problem regarding OLDER 2.5" drive models of above a certain capacity drawing more current, and that was the reason why you couldn't originally install them in many laptops that had no bios restriction regarding the max capacity that could be recognized, but that did NOT apply to current drives.

The circuits of the external drive's (drive enclosure's) board the hard drive itself connects to inside the enclosure draw very little current, so that can almost be ignored - it's the hard drive itself inside the enclosure that draws the lion's share of the current.

All conventional 2.5" drives that I've examined the specs for (I looked at them for several current drive lines today too) draw more than 500 ma when the drive is initially spinning up, but that can be ignored providing that isn't more than say, 1 amp, because the USB 1.x and USB 2.0 circuits that can actually supply the max USB spec 500 ma will handle that for a brief time. The hard drive itself always draws the most current when it's initially spinning up, but once it's spinning it's full speed the current required is much less.

If the continuous or average current required for the hard drive itself ./ the external hard drive in total is less than 500 ma, it will work fine with the USB 1.x and USB 2.0 circuits that can actually supply the max USB spec 500 ma.
.....

Now there are SATA III 2.5" hard drives, external enclosures that support USB 3.0 specs. pre-packaged external drives that support USB 3.0 specs, and USB controllers that support USB 3.0 specs.
USB 3.0 specs have upped the current a USB 3.0 port is supposed to be able to supply per port to 900 ma max.

However, I haven't seen ANY external enclosures for (single) 2.5" drives, pre-packaged external drives (with one hard drive inside), that are USB 3.0 capable, that are USB 3.0 compatible ONLY - they've all been USB 2.0 backward compatible.

e.g.
If a pre-packaged "portable" (2.5") external hard drive (with one hard drive inside of it) that supports USB 3.0 AND USB 2.0 specs does not come with an external power adapter you must plug into the enclosure, the external drive will work fine with the USB 1.x and USB 2.0 circuits that can actually supply the max USB spec 500 ma, although the max burst data transfer speed will be that of the USB 1.x or USB 2.0 specs. .
.........

E.g.

I have a 2.5" SATA II hard drive I bought at the same time I bought the drives for my friend's laptops - it's installed in a Vantec external enclosure that supports either a USB 2.0 or a eSATA connection.
The Vantec enclosure comes with a USB Y cord that can connect to two USB ports on a computer, but the external hard drive enclosure works fine with that hard drive installed in it connected to one USB port on a computer that can actually supply 500 ma of current.

Max continuous power available from a USB port that can supply 500 ma is 5v x .500 amps (500 ma) = 2.5 watts

Momentus 5400.6 series data sheet
http://www.seagate.com/docs/pdf/dat...

Power Management

Startup Current 5v (amps max) 1.0

Power Mgmt (W)
Seek 1.54
Read/Write 2.6 / 2.85
Idle/Standby .81 / .22

However, what's most important is the continuous or average current draw / wattage, not what the "peak" is the drive briefly requires....

Momentus 5400.6 SATA 3Gb/s 500-GB Hard Drive
ST9500325AS
Specifications
http://www.seagate.com/ww/v/index.j...

POWER
5V start max current 1.0A
Average idle power 1.40W (0.28 a or 280 ma @ 5v)
Average operating power 1.78W (0.358 a or 358 ma @ 5v)
Average seek power 1.54W ( 0.308 a or 308 ma @ 5v)

On the label on the drive itself it says:
+5v 0.451 a
- (2.25 watts) - probably = the max continuous current / wattage

........

A current drive, SATA III ....

Seagate Momentus XT series data sheet
http://www.seagate.com/docs/pdf/dat...

Solid State Hybrid Drives

ST750LX003 / ST95005620AS

Power management

Power(W)

750 gb / 500 gb drive

Seek 3.3 / 2.2

Idle 1.1 / 0.8

At bottom of data sheet - Copyright 2012
.....

However, what's most important is the continuous or average current draw / wattage, not what the "peak" is the drive briefly requires....


Momentus® XT Solid State Hybrid Drives
ST750LX003
Specifications
http://www.seagate.com/www/en-au/pr...

POWER
5V start max current 1.0A
Average idle power 0.8W
Average operating power 1.1W
Average seek power 2.2W
..........

That drive will probably work fine with the USB 1.x and USB 2.0 circuits that can actually supply the max USB spec 500 ma, although the max burst data transfer speed will be that of the USB 1.x or USB 2.0 specs. .
....

.


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