Is it safe to use a micro-USB 2 cable in a USB 3 portable hard drive?











up vote
22
down vote

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1












The micro-B USB 3 port seems to be somewhat backwards compatible with the old micro-USB 2 standard. I was able to charge a phone that had the micro-B USB 3 port with a micro-USB 2 cable.



However, I am not sure to what extent this is a part of the USB standard or just something the phone manufacturer did for backwards compatibility.



I have a hard drive that uses micro-B USB 3. Would it be safe to use the USB 2 standard cable to read/power the hard drive?



ie. Use this cable for this port.
Micro-B USB 2 cableMicro-B USB 3 port










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  • 3




    @RicardoS. See grawity's answer, the extra connectors bring extra transmission lines. So it will work, albeit at USB 2.0 speeds. pinoutguide.com/PortableDevices/…
    – Daniel F
    Nov 20 at 8:58

















up vote
22
down vote

favorite
1












The micro-B USB 3 port seems to be somewhat backwards compatible with the old micro-USB 2 standard. I was able to charge a phone that had the micro-B USB 3 port with a micro-USB 2 cable.



However, I am not sure to what extent this is a part of the USB standard or just something the phone manufacturer did for backwards compatibility.



I have a hard drive that uses micro-B USB 3. Would it be safe to use the USB 2 standard cable to read/power the hard drive?



ie. Use this cable for this port.
Micro-B USB 2 cableMicro-B USB 3 port










share|improve this question


















  • 3




    @RicardoS. See grawity's answer, the extra connectors bring extra transmission lines. So it will work, albeit at USB 2.0 speeds. pinoutguide.com/PortableDevices/…
    – Daniel F
    Nov 20 at 8:58















up vote
22
down vote

favorite
1









up vote
22
down vote

favorite
1






1





The micro-B USB 3 port seems to be somewhat backwards compatible with the old micro-USB 2 standard. I was able to charge a phone that had the micro-B USB 3 port with a micro-USB 2 cable.



However, I am not sure to what extent this is a part of the USB standard or just something the phone manufacturer did for backwards compatibility.



I have a hard drive that uses micro-B USB 3. Would it be safe to use the USB 2 standard cable to read/power the hard drive?



ie. Use this cable for this port.
Micro-B USB 2 cableMicro-B USB 3 port










share|improve this question













The micro-B USB 3 port seems to be somewhat backwards compatible with the old micro-USB 2 standard. I was able to charge a phone that had the micro-B USB 3 port with a micro-USB 2 cable.



However, I am not sure to what extent this is a part of the USB standard or just something the phone manufacturer did for backwards compatibility.



I have a hard drive that uses micro-B USB 3. Would it be safe to use the USB 2 standard cable to read/power the hard drive?



ie. Use this cable for this port.
Micro-B USB 2 cableMicro-B USB 3 port







usb cable usb-storage usb-3 usb-2






share|improve this question













share|improve this question











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share|improve this question










asked Nov 20 at 7:20









juil

259311




259311








  • 3




    @RicardoS. See grawity's answer, the extra connectors bring extra transmission lines. So it will work, albeit at USB 2.0 speeds. pinoutguide.com/PortableDevices/…
    – Daniel F
    Nov 20 at 8:58
















  • 3




    @RicardoS. See grawity's answer, the extra connectors bring extra transmission lines. So it will work, albeit at USB 2.0 speeds. pinoutguide.com/PortableDevices/…
    – Daniel F
    Nov 20 at 8:58










3




3




@RicardoS. See grawity's answer, the extra connectors bring extra transmission lines. So it will work, albeit at USB 2.0 speeds. pinoutguide.com/PortableDevices/…
– Daniel F
Nov 20 at 8:58






@RicardoS. See grawity's answer, the extra connectors bring extra transmission lines. So it will work, albeit at USB 2.0 speeds. pinoutguide.com/PortableDevices/…
– Daniel F
Nov 20 at 8:58












3 Answers
3






active

oldest

votes

















up vote
33
down vote



accepted










Yes, it's safe. The base connector is identical to the original Micro-B, only adding the USB 3.0 data send/receive lines on the side. (USB 3.0 is backwards-compatible with 2.0, and this applies equally to all connectors it introduced – both the full-size and micro-size, type-A and type-B ports).



The end result will generally be the same as if connecting the drive to a computer's USB 2.0 port (which doesn't have these extra pins, either) – you'll be limited to the speed and power that USB 2.0 allows and won't be able to use UAS, but it should still work properly otherwise.



The extra pins are differential signal pairs (RX+, RX-, TX+, TX-, ground). Compare pinouts for:




  • USB 2.0 Type-A/B and 3.0 Type-A/B

  • USB 2.0 Micro-A/B and 3.0 Micro-A/B

  • The official cable & connector specification is available from USB-IF for free.


Be sure to use a decent cable though, as magnetic disks will probably need the full 500 mA that a USB 2.0 port normally provides. Original phone cables should work fine (modern phones draw several times more anyway), but some cheap replacement cables might be unable to power the HDD at all, or it might repeatedly shut down while in use.






share|improve this answer



















  • 2




    adding to that, the USB 3.0 port is specified to provide at least 0.9A current (4.5W power), but no guarantee it's still available with USB 2.0 cable.
    – iBug
    Nov 20 at 8:52






  • 4




    @iBug: Yes, but the devices already have to expect to be plugged into a computer's 2.0-only port, which as far as I know won't provide more than 0.5A regardless of cable – which is enough at least for the 2.5" HDDs that I've seen.
    – grawity
    Nov 20 at 9:10












  • please note that depending on the USB2.0 Port you might not even get the specced 500mA at one port without issues like disconnecting devices or instable usage.
    – Dennis Nolte
    2 days ago










  • Okay, so data speeds will obviously be impacted, and it's just a matter of making sure that enough power can be drawn through the cable?
    – juil
    5 hours ago


















up vote
10
down vote













Yes, and no, with a small caveat.



Generally, this will work, and is perfectly safe (albeit considerably slower than using an USB 3 cable).



However, note that some disks require use too much power for USB 2.0 to be sufficient. While the amount of power that you can draw from USB 3 is quite amazing, USB 2.0 is kinda puny in that respect. There are disks which aren't happy with that.



This is still "safe" operation insofar as there is no way you could damage the disk (or the computer) by doing so, but it is not safe insofar as writing data might not be 100% reliable. Actually, it should either work or not work (in particular because spinning up successfully takes the most power), but you cannot be 100% sure. Writing does use more power than idling, and you never know for certain what goes on when a device is slightly under-powered. Generally, though, no worries. Usually it just does work or doesn't, so you can easily tell (all or nothing!), and most modern disks will be in the "just works" camp.



A workaround that is sometimes applied is using a Y-cable which sucks power from two USB 2.0 ports (but only uses one to transmit data). This is strictly a violation of the standard, but it "works fine".

Of course, this is only an applicable solution if you already happen to have one of these lying around (and maybe don't know what they're good for?) because a Y-cable is more expensive to buy than a proper USB 3 cable which will work within the specification and at USB 3 speed...






share|improve this answer





















  • I thought that USB power negotiation worked such that if the requested current isn't available, then that particular configuration isn't activated - i.e. a device that can't work on USB 2 power levels just won't operate, because the host won't find a configuration it can support.
    – Toby Speight
    Nov 20 at 11:11






  • 4




    In theory, all devices must start at "one unit load" which is 150mA for USB3 and 100mA for USB2 (the USB3 device can detect absence of cables), and can then demand 5x as much. In practice, you get all kinds of funny stuff on every end (including host, adapter, and disks). I have an old 840evo which is officially rated "2.2W" (so at 5V well below 500mA) and has 0.86A @ 5V written on its back (WTF?) connected to my good old Wii U. The disk demonstrably pulls 0.1A idle and below 0.45A when writing, but without Y-cable the LED on the USB-SATA connector will go on, yet nothing else happens.
    – Damon
    Nov 20 at 12:47










  • USB just sucks... unluckily there's nothing better :D
    – Damon
    Nov 20 at 12:47










  • Spinning disks will draw much more power when spinning up, so even a disk which is content with 100mA in idle and ~450mA when being accessed will simply refuse to work when it doesn't get sufficient current to "take off" (start to spin). Apparently, no one ever thought about adding a small rechargeable battery to an enclosure, just to provide the extra bit of start-up current. Recharging would happen when the disk is spinning and the head is idle, possibly in less than a minute.
    – Klaws
    yesterday


















up vote
3
down vote













Yes I can verify this works as I have tested this myself.



I have done this exact same thing with a WD Elements 2TB USB3 portable hard drive and multiple decent quality USB2 micro B cables without problems. But indeed it will be at USB2 speeds.






share|improve this answer





















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    3 Answers
    3






    active

    oldest

    votes








    3 Answers
    3






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes








    up vote
    33
    down vote



    accepted










    Yes, it's safe. The base connector is identical to the original Micro-B, only adding the USB 3.0 data send/receive lines on the side. (USB 3.0 is backwards-compatible with 2.0, and this applies equally to all connectors it introduced – both the full-size and micro-size, type-A and type-B ports).



    The end result will generally be the same as if connecting the drive to a computer's USB 2.0 port (which doesn't have these extra pins, either) – you'll be limited to the speed and power that USB 2.0 allows and won't be able to use UAS, but it should still work properly otherwise.



    The extra pins are differential signal pairs (RX+, RX-, TX+, TX-, ground). Compare pinouts for:




    • USB 2.0 Type-A/B and 3.0 Type-A/B

    • USB 2.0 Micro-A/B and 3.0 Micro-A/B

    • The official cable & connector specification is available from USB-IF for free.


    Be sure to use a decent cable though, as magnetic disks will probably need the full 500 mA that a USB 2.0 port normally provides. Original phone cables should work fine (modern phones draw several times more anyway), but some cheap replacement cables might be unable to power the HDD at all, or it might repeatedly shut down while in use.






    share|improve this answer



















    • 2




      adding to that, the USB 3.0 port is specified to provide at least 0.9A current (4.5W power), but no guarantee it's still available with USB 2.0 cable.
      – iBug
      Nov 20 at 8:52






    • 4




      @iBug: Yes, but the devices already have to expect to be plugged into a computer's 2.0-only port, which as far as I know won't provide more than 0.5A regardless of cable – which is enough at least for the 2.5" HDDs that I've seen.
      – grawity
      Nov 20 at 9:10












    • please note that depending on the USB2.0 Port you might not even get the specced 500mA at one port without issues like disconnecting devices or instable usage.
      – Dennis Nolte
      2 days ago










    • Okay, so data speeds will obviously be impacted, and it's just a matter of making sure that enough power can be drawn through the cable?
      – juil
      5 hours ago















    up vote
    33
    down vote



    accepted










    Yes, it's safe. The base connector is identical to the original Micro-B, only adding the USB 3.0 data send/receive lines on the side. (USB 3.0 is backwards-compatible with 2.0, and this applies equally to all connectors it introduced – both the full-size and micro-size, type-A and type-B ports).



    The end result will generally be the same as if connecting the drive to a computer's USB 2.0 port (which doesn't have these extra pins, either) – you'll be limited to the speed and power that USB 2.0 allows and won't be able to use UAS, but it should still work properly otherwise.



    The extra pins are differential signal pairs (RX+, RX-, TX+, TX-, ground). Compare pinouts for:




    • USB 2.0 Type-A/B and 3.0 Type-A/B

    • USB 2.0 Micro-A/B and 3.0 Micro-A/B

    • The official cable & connector specification is available from USB-IF for free.


    Be sure to use a decent cable though, as magnetic disks will probably need the full 500 mA that a USB 2.0 port normally provides. Original phone cables should work fine (modern phones draw several times more anyway), but some cheap replacement cables might be unable to power the HDD at all, or it might repeatedly shut down while in use.






    share|improve this answer



















    • 2




      adding to that, the USB 3.0 port is specified to provide at least 0.9A current (4.5W power), but no guarantee it's still available with USB 2.0 cable.
      – iBug
      Nov 20 at 8:52






    • 4




      @iBug: Yes, but the devices already have to expect to be plugged into a computer's 2.0-only port, which as far as I know won't provide more than 0.5A regardless of cable – which is enough at least for the 2.5" HDDs that I've seen.
      – grawity
      Nov 20 at 9:10












    • please note that depending on the USB2.0 Port you might not even get the specced 500mA at one port without issues like disconnecting devices or instable usage.
      – Dennis Nolte
      2 days ago










    • Okay, so data speeds will obviously be impacted, and it's just a matter of making sure that enough power can be drawn through the cable?
      – juil
      5 hours ago













    up vote
    33
    down vote



    accepted







    up vote
    33
    down vote



    accepted






    Yes, it's safe. The base connector is identical to the original Micro-B, only adding the USB 3.0 data send/receive lines on the side. (USB 3.0 is backwards-compatible with 2.0, and this applies equally to all connectors it introduced – both the full-size and micro-size, type-A and type-B ports).



    The end result will generally be the same as if connecting the drive to a computer's USB 2.0 port (which doesn't have these extra pins, either) – you'll be limited to the speed and power that USB 2.0 allows and won't be able to use UAS, but it should still work properly otherwise.



    The extra pins are differential signal pairs (RX+, RX-, TX+, TX-, ground). Compare pinouts for:




    • USB 2.0 Type-A/B and 3.0 Type-A/B

    • USB 2.0 Micro-A/B and 3.0 Micro-A/B

    • The official cable & connector specification is available from USB-IF for free.


    Be sure to use a decent cable though, as magnetic disks will probably need the full 500 mA that a USB 2.0 port normally provides. Original phone cables should work fine (modern phones draw several times more anyway), but some cheap replacement cables might be unable to power the HDD at all, or it might repeatedly shut down while in use.






    share|improve this answer














    Yes, it's safe. The base connector is identical to the original Micro-B, only adding the USB 3.0 data send/receive lines on the side. (USB 3.0 is backwards-compatible with 2.0, and this applies equally to all connectors it introduced – both the full-size and micro-size, type-A and type-B ports).



    The end result will generally be the same as if connecting the drive to a computer's USB 2.0 port (which doesn't have these extra pins, either) – you'll be limited to the speed and power that USB 2.0 allows and won't be able to use UAS, but it should still work properly otherwise.



    The extra pins are differential signal pairs (RX+, RX-, TX+, TX-, ground). Compare pinouts for:




    • USB 2.0 Type-A/B and 3.0 Type-A/B

    • USB 2.0 Micro-A/B and 3.0 Micro-A/B

    • The official cable & connector specification is available from USB-IF for free.


    Be sure to use a decent cable though, as magnetic disks will probably need the full 500 mA that a USB 2.0 port normally provides. Original phone cables should work fine (modern phones draw several times more anyway), but some cheap replacement cables might be unable to power the HDD at all, or it might repeatedly shut down while in use.







    share|improve this answer














    share|improve this answer



    share|improve this answer








    edited Nov 20 at 10:25

























    answered Nov 20 at 8:12









    grawity

    228k35481540




    228k35481540








    • 2




      adding to that, the USB 3.0 port is specified to provide at least 0.9A current (4.5W power), but no guarantee it's still available with USB 2.0 cable.
      – iBug
      Nov 20 at 8:52






    • 4




      @iBug: Yes, but the devices already have to expect to be plugged into a computer's 2.0-only port, which as far as I know won't provide more than 0.5A regardless of cable – which is enough at least for the 2.5" HDDs that I've seen.
      – grawity
      Nov 20 at 9:10












    • please note that depending on the USB2.0 Port you might not even get the specced 500mA at one port without issues like disconnecting devices or instable usage.
      – Dennis Nolte
      2 days ago










    • Okay, so data speeds will obviously be impacted, and it's just a matter of making sure that enough power can be drawn through the cable?
      – juil
      5 hours ago














    • 2




      adding to that, the USB 3.0 port is specified to provide at least 0.9A current (4.5W power), but no guarantee it's still available with USB 2.0 cable.
      – iBug
      Nov 20 at 8:52






    • 4




      @iBug: Yes, but the devices already have to expect to be plugged into a computer's 2.0-only port, which as far as I know won't provide more than 0.5A regardless of cable – which is enough at least for the 2.5" HDDs that I've seen.
      – grawity
      Nov 20 at 9:10












    • please note that depending on the USB2.0 Port you might not even get the specced 500mA at one port without issues like disconnecting devices or instable usage.
      – Dennis Nolte
      2 days ago










    • Okay, so data speeds will obviously be impacted, and it's just a matter of making sure that enough power can be drawn through the cable?
      – juil
      5 hours ago








    2




    2




    adding to that, the USB 3.0 port is specified to provide at least 0.9A current (4.5W power), but no guarantee it's still available with USB 2.0 cable.
    – iBug
    Nov 20 at 8:52




    adding to that, the USB 3.0 port is specified to provide at least 0.9A current (4.5W power), but no guarantee it's still available with USB 2.0 cable.
    – iBug
    Nov 20 at 8:52




    4




    4




    @iBug: Yes, but the devices already have to expect to be plugged into a computer's 2.0-only port, which as far as I know won't provide more than 0.5A regardless of cable – which is enough at least for the 2.5" HDDs that I've seen.
    – grawity
    Nov 20 at 9:10






    @iBug: Yes, but the devices already have to expect to be plugged into a computer's 2.0-only port, which as far as I know won't provide more than 0.5A regardless of cable – which is enough at least for the 2.5" HDDs that I've seen.
    – grawity
    Nov 20 at 9:10














    please note that depending on the USB2.0 Port you might not even get the specced 500mA at one port without issues like disconnecting devices or instable usage.
    – Dennis Nolte
    2 days ago




    please note that depending on the USB2.0 Port you might not even get the specced 500mA at one port without issues like disconnecting devices or instable usage.
    – Dennis Nolte
    2 days ago












    Okay, so data speeds will obviously be impacted, and it's just a matter of making sure that enough power can be drawn through the cable?
    – juil
    5 hours ago




    Okay, so data speeds will obviously be impacted, and it's just a matter of making sure that enough power can be drawn through the cable?
    – juil
    5 hours ago












    up vote
    10
    down vote













    Yes, and no, with a small caveat.



    Generally, this will work, and is perfectly safe (albeit considerably slower than using an USB 3 cable).



    However, note that some disks require use too much power for USB 2.0 to be sufficient. While the amount of power that you can draw from USB 3 is quite amazing, USB 2.0 is kinda puny in that respect. There are disks which aren't happy with that.



    This is still "safe" operation insofar as there is no way you could damage the disk (or the computer) by doing so, but it is not safe insofar as writing data might not be 100% reliable. Actually, it should either work or not work (in particular because spinning up successfully takes the most power), but you cannot be 100% sure. Writing does use more power than idling, and you never know for certain what goes on when a device is slightly under-powered. Generally, though, no worries. Usually it just does work or doesn't, so you can easily tell (all or nothing!), and most modern disks will be in the "just works" camp.



    A workaround that is sometimes applied is using a Y-cable which sucks power from two USB 2.0 ports (but only uses one to transmit data). This is strictly a violation of the standard, but it "works fine".

    Of course, this is only an applicable solution if you already happen to have one of these lying around (and maybe don't know what they're good for?) because a Y-cable is more expensive to buy than a proper USB 3 cable which will work within the specification and at USB 3 speed...






    share|improve this answer





















    • I thought that USB power negotiation worked such that if the requested current isn't available, then that particular configuration isn't activated - i.e. a device that can't work on USB 2 power levels just won't operate, because the host won't find a configuration it can support.
      – Toby Speight
      Nov 20 at 11:11






    • 4




      In theory, all devices must start at "one unit load" which is 150mA for USB3 and 100mA for USB2 (the USB3 device can detect absence of cables), and can then demand 5x as much. In practice, you get all kinds of funny stuff on every end (including host, adapter, and disks). I have an old 840evo which is officially rated "2.2W" (so at 5V well below 500mA) and has 0.86A @ 5V written on its back (WTF?) connected to my good old Wii U. The disk demonstrably pulls 0.1A idle and below 0.45A when writing, but without Y-cable the LED on the USB-SATA connector will go on, yet nothing else happens.
      – Damon
      Nov 20 at 12:47










    • USB just sucks... unluckily there's nothing better :D
      – Damon
      Nov 20 at 12:47










    • Spinning disks will draw much more power when spinning up, so even a disk which is content with 100mA in idle and ~450mA when being accessed will simply refuse to work when it doesn't get sufficient current to "take off" (start to spin). Apparently, no one ever thought about adding a small rechargeable battery to an enclosure, just to provide the extra bit of start-up current. Recharging would happen when the disk is spinning and the head is idle, possibly in less than a minute.
      – Klaws
      yesterday















    up vote
    10
    down vote













    Yes, and no, with a small caveat.



    Generally, this will work, and is perfectly safe (albeit considerably slower than using an USB 3 cable).



    However, note that some disks require use too much power for USB 2.0 to be sufficient. While the amount of power that you can draw from USB 3 is quite amazing, USB 2.0 is kinda puny in that respect. There are disks which aren't happy with that.



    This is still "safe" operation insofar as there is no way you could damage the disk (or the computer) by doing so, but it is not safe insofar as writing data might not be 100% reliable. Actually, it should either work or not work (in particular because spinning up successfully takes the most power), but you cannot be 100% sure. Writing does use more power than idling, and you never know for certain what goes on when a device is slightly under-powered. Generally, though, no worries. Usually it just does work or doesn't, so you can easily tell (all or nothing!), and most modern disks will be in the "just works" camp.



    A workaround that is sometimes applied is using a Y-cable which sucks power from two USB 2.0 ports (but only uses one to transmit data). This is strictly a violation of the standard, but it "works fine".

    Of course, this is only an applicable solution if you already happen to have one of these lying around (and maybe don't know what they're good for?) because a Y-cable is more expensive to buy than a proper USB 3 cable which will work within the specification and at USB 3 speed...






    share|improve this answer





















    • I thought that USB power negotiation worked such that if the requested current isn't available, then that particular configuration isn't activated - i.e. a device that can't work on USB 2 power levels just won't operate, because the host won't find a configuration it can support.
      – Toby Speight
      Nov 20 at 11:11






    • 4




      In theory, all devices must start at "one unit load" which is 150mA for USB3 and 100mA for USB2 (the USB3 device can detect absence of cables), and can then demand 5x as much. In practice, you get all kinds of funny stuff on every end (including host, adapter, and disks). I have an old 840evo which is officially rated "2.2W" (so at 5V well below 500mA) and has 0.86A @ 5V written on its back (WTF?) connected to my good old Wii U. The disk demonstrably pulls 0.1A idle and below 0.45A when writing, but without Y-cable the LED on the USB-SATA connector will go on, yet nothing else happens.
      – Damon
      Nov 20 at 12:47










    • USB just sucks... unluckily there's nothing better :D
      – Damon
      Nov 20 at 12:47










    • Spinning disks will draw much more power when spinning up, so even a disk which is content with 100mA in idle and ~450mA when being accessed will simply refuse to work when it doesn't get sufficient current to "take off" (start to spin). Apparently, no one ever thought about adding a small rechargeable battery to an enclosure, just to provide the extra bit of start-up current. Recharging would happen when the disk is spinning and the head is idle, possibly in less than a minute.
      – Klaws
      yesterday













    up vote
    10
    down vote










    up vote
    10
    down vote









    Yes, and no, with a small caveat.



    Generally, this will work, and is perfectly safe (albeit considerably slower than using an USB 3 cable).



    However, note that some disks require use too much power for USB 2.0 to be sufficient. While the amount of power that you can draw from USB 3 is quite amazing, USB 2.0 is kinda puny in that respect. There are disks which aren't happy with that.



    This is still "safe" operation insofar as there is no way you could damage the disk (or the computer) by doing so, but it is not safe insofar as writing data might not be 100% reliable. Actually, it should either work or not work (in particular because spinning up successfully takes the most power), but you cannot be 100% sure. Writing does use more power than idling, and you never know for certain what goes on when a device is slightly under-powered. Generally, though, no worries. Usually it just does work or doesn't, so you can easily tell (all or nothing!), and most modern disks will be in the "just works" camp.



    A workaround that is sometimes applied is using a Y-cable which sucks power from two USB 2.0 ports (but only uses one to transmit data). This is strictly a violation of the standard, but it "works fine".

    Of course, this is only an applicable solution if you already happen to have one of these lying around (and maybe don't know what they're good for?) because a Y-cable is more expensive to buy than a proper USB 3 cable which will work within the specification and at USB 3 speed...






    share|improve this answer












    Yes, and no, with a small caveat.



    Generally, this will work, and is perfectly safe (albeit considerably slower than using an USB 3 cable).



    However, note that some disks require use too much power for USB 2.0 to be sufficient. While the amount of power that you can draw from USB 3 is quite amazing, USB 2.0 is kinda puny in that respect. There are disks which aren't happy with that.



    This is still "safe" operation insofar as there is no way you could damage the disk (or the computer) by doing so, but it is not safe insofar as writing data might not be 100% reliable. Actually, it should either work or not work (in particular because spinning up successfully takes the most power), but you cannot be 100% sure. Writing does use more power than idling, and you never know for certain what goes on when a device is slightly under-powered. Generally, though, no worries. Usually it just does work or doesn't, so you can easily tell (all or nothing!), and most modern disks will be in the "just works" camp.



    A workaround that is sometimes applied is using a Y-cable which sucks power from two USB 2.0 ports (but only uses one to transmit data). This is strictly a violation of the standard, but it "works fine".

    Of course, this is only an applicable solution if you already happen to have one of these lying around (and maybe don't know what they're good for?) because a Y-cable is more expensive to buy than a proper USB 3 cable which will work within the specification and at USB 3 speed...







    share|improve this answer












    share|improve this answer



    share|improve this answer










    answered Nov 20 at 10:13









    Damon

    3,47031624




    3,47031624












    • I thought that USB power negotiation worked such that if the requested current isn't available, then that particular configuration isn't activated - i.e. a device that can't work on USB 2 power levels just won't operate, because the host won't find a configuration it can support.
      – Toby Speight
      Nov 20 at 11:11






    • 4




      In theory, all devices must start at "one unit load" which is 150mA for USB3 and 100mA for USB2 (the USB3 device can detect absence of cables), and can then demand 5x as much. In practice, you get all kinds of funny stuff on every end (including host, adapter, and disks). I have an old 840evo which is officially rated "2.2W" (so at 5V well below 500mA) and has 0.86A @ 5V written on its back (WTF?) connected to my good old Wii U. The disk demonstrably pulls 0.1A idle and below 0.45A when writing, but without Y-cable the LED on the USB-SATA connector will go on, yet nothing else happens.
      – Damon
      Nov 20 at 12:47










    • USB just sucks... unluckily there's nothing better :D
      – Damon
      Nov 20 at 12:47










    • Spinning disks will draw much more power when spinning up, so even a disk which is content with 100mA in idle and ~450mA when being accessed will simply refuse to work when it doesn't get sufficient current to "take off" (start to spin). Apparently, no one ever thought about adding a small rechargeable battery to an enclosure, just to provide the extra bit of start-up current. Recharging would happen when the disk is spinning and the head is idle, possibly in less than a minute.
      – Klaws
      yesterday


















    • I thought that USB power negotiation worked such that if the requested current isn't available, then that particular configuration isn't activated - i.e. a device that can't work on USB 2 power levels just won't operate, because the host won't find a configuration it can support.
      – Toby Speight
      Nov 20 at 11:11






    • 4




      In theory, all devices must start at "one unit load" which is 150mA for USB3 and 100mA for USB2 (the USB3 device can detect absence of cables), and can then demand 5x as much. In practice, you get all kinds of funny stuff on every end (including host, adapter, and disks). I have an old 840evo which is officially rated "2.2W" (so at 5V well below 500mA) and has 0.86A @ 5V written on its back (WTF?) connected to my good old Wii U. The disk demonstrably pulls 0.1A idle and below 0.45A when writing, but without Y-cable the LED on the USB-SATA connector will go on, yet nothing else happens.
      – Damon
      Nov 20 at 12:47










    • USB just sucks... unluckily there's nothing better :D
      – Damon
      Nov 20 at 12:47










    • Spinning disks will draw much more power when spinning up, so even a disk which is content with 100mA in idle and ~450mA when being accessed will simply refuse to work when it doesn't get sufficient current to "take off" (start to spin). Apparently, no one ever thought about adding a small rechargeable battery to an enclosure, just to provide the extra bit of start-up current. Recharging would happen when the disk is spinning and the head is idle, possibly in less than a minute.
      – Klaws
      yesterday
















    I thought that USB power negotiation worked such that if the requested current isn't available, then that particular configuration isn't activated - i.e. a device that can't work on USB 2 power levels just won't operate, because the host won't find a configuration it can support.
    – Toby Speight
    Nov 20 at 11:11




    I thought that USB power negotiation worked such that if the requested current isn't available, then that particular configuration isn't activated - i.e. a device that can't work on USB 2 power levels just won't operate, because the host won't find a configuration it can support.
    – Toby Speight
    Nov 20 at 11:11




    4




    4




    In theory, all devices must start at "one unit load" which is 150mA for USB3 and 100mA for USB2 (the USB3 device can detect absence of cables), and can then demand 5x as much. In practice, you get all kinds of funny stuff on every end (including host, adapter, and disks). I have an old 840evo which is officially rated "2.2W" (so at 5V well below 500mA) and has 0.86A @ 5V written on its back (WTF?) connected to my good old Wii U. The disk demonstrably pulls 0.1A idle and below 0.45A when writing, but without Y-cable the LED on the USB-SATA connector will go on, yet nothing else happens.
    – Damon
    Nov 20 at 12:47




    In theory, all devices must start at "one unit load" which is 150mA for USB3 and 100mA for USB2 (the USB3 device can detect absence of cables), and can then demand 5x as much. In practice, you get all kinds of funny stuff on every end (including host, adapter, and disks). I have an old 840evo which is officially rated "2.2W" (so at 5V well below 500mA) and has 0.86A @ 5V written on its back (WTF?) connected to my good old Wii U. The disk demonstrably pulls 0.1A idle and below 0.45A when writing, but without Y-cable the LED on the USB-SATA connector will go on, yet nothing else happens.
    – Damon
    Nov 20 at 12:47












    USB just sucks... unluckily there's nothing better :D
    – Damon
    Nov 20 at 12:47




    USB just sucks... unluckily there's nothing better :D
    – Damon
    Nov 20 at 12:47












    Spinning disks will draw much more power when spinning up, so even a disk which is content with 100mA in idle and ~450mA when being accessed will simply refuse to work when it doesn't get sufficient current to "take off" (start to spin). Apparently, no one ever thought about adding a small rechargeable battery to an enclosure, just to provide the extra bit of start-up current. Recharging would happen when the disk is spinning and the head is idle, possibly in less than a minute.
    – Klaws
    yesterday




    Spinning disks will draw much more power when spinning up, so even a disk which is content with 100mA in idle and ~450mA when being accessed will simply refuse to work when it doesn't get sufficient current to "take off" (start to spin). Apparently, no one ever thought about adding a small rechargeable battery to an enclosure, just to provide the extra bit of start-up current. Recharging would happen when the disk is spinning and the head is idle, possibly in less than a minute.
    – Klaws
    yesterday










    up vote
    3
    down vote













    Yes I can verify this works as I have tested this myself.



    I have done this exact same thing with a WD Elements 2TB USB3 portable hard drive and multiple decent quality USB2 micro B cables without problems. But indeed it will be at USB2 speeds.






    share|improve this answer

























      up vote
      3
      down vote













      Yes I can verify this works as I have tested this myself.



      I have done this exact same thing with a WD Elements 2TB USB3 portable hard drive and multiple decent quality USB2 micro B cables without problems. But indeed it will be at USB2 speeds.






      share|improve this answer























        up vote
        3
        down vote










        up vote
        3
        down vote









        Yes I can verify this works as I have tested this myself.



        I have done this exact same thing with a WD Elements 2TB USB3 portable hard drive and multiple decent quality USB2 micro B cables without problems. But indeed it will be at USB2 speeds.






        share|improve this answer












        Yes I can verify this works as I have tested this myself.



        I have done this exact same thing with a WD Elements 2TB USB3 portable hard drive and multiple decent quality USB2 micro B cables without problems. But indeed it will be at USB2 speeds.







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered Nov 20 at 12:37









        Matthias Duyck

        311




        311






























             

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