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Thread: Slow USB drive

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    Slow USB drive

    I just bought a USB 3.0 flash drive that says it can transfer at 120 MB/s, and I formatted it as NTFS so I can copy a large (16 GB) file onto it. When I start copying the large file from my laptop (Dell Inspiron 7520 with Windows 7 Pro) to the flash drive, it starts at around 100 MB/s and says it will take around 3 minutes, but after a few seconds, it slows down to around 15 MB/s and says it will take around 20 minutes, which it does, and anything else running on the laptop during the copy slows way down. Also, if I click on the Cancel button to stop the copy, it takes a couple of minutes or more before the cancelling finishes.

    The drive is brand new, and the same thing happens with a SanDisk 16 GB USB drive that I have, so the drives are not faulty, and this doesn't happen with smaller files under around 1 GB on either drive. Is something wrong somewhere, or is there an inherent speed limitation somewhere when copying large files?

    (My laptop has four USB sockets: how can I tell what USB level each one is?)

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    USB 3 sockets are (usually) blue. Check you have the cable in the correct socket.
    Your machine shouldn't slow down other things during the copy and cancel shouldn't take more than a few seconds. Check that the USB drivers are up to date - go to the machine manufacturer's web site.

    cheers, Paul

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    Super Moderator Rick Corbett's Avatar
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    The Quickstart Guide for the Inspiron 7520 shows all 4 USB sockets are USB3, with one (rearmost on the left side) labelled PowerShare (i.e. to charge other devices).

    Nir Sofer's USBDeview (small, free, standalone) will show you what speed devices are connected at. Just check the USB Version column. You can also right-click on a connected device and carry out a speed test.
    usbdeview-speed1.png
    Click to enlarge

    (I've just checked my own Dell laptop and all 3 of the USB3 sockets are black. It would be great if manufacturers could be consistent. It's just so much quicker to check the colour of the socket rather than having to hunt down the manual(s).)

    Hope this helps...

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    You will find that there have been a number of discussions on USB speeds and to say that it can be inconsistent is sometimes an understatement.

    A PC will often have one or two USB ports that are directly on the MB and additional ones that are an internal hub. The direct ones can be faster than the ones on the hub. On a desktop PC, the ones in the front are often on a hub.

    Also, it's possible that your Anti-Virus is slowing you down by checking everything that's being written to the USB device. Not sure you can override that or not.
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    Yup, try a different USB port on a different side of the machine. If you are plugging the drive into side now, try a back port. Ports on the same side of the computer are likely plugged into the same (or similar) motherboard header. Ports on a different side have a better chance of using a different MB header with different capabilities.

    And it's worth examining the USB sockets on the computer too. It's something of a convention that USB 3 sockets are blue, but really you are looking for any colour different from the socket you are currently using.

    Daisy-chaining hubs, splitters/repeaters/extenders, all can cause varying performance levels. My take on it, USB is designed more for convenience and flexibility than it is for consistent performance. And for a lot of USB devices, a low speed data connection just isn't a problem. For a mass storage device though, that's when you want high throughput.

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    Super Moderator CLiNT's Avatar
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    Don't plan on getting a sustained 120mb/s, you might at best get small short bursts, then it's back to the sea floor.
    USB speeds are neither consistent or reliable.
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    Thanks for your replies.

    The laptop has four USB sockets, all blue, and according to the USBDeview utility, all USB 3.0, and (and according to the USBDeview utility's speed test) all reading at around 100 MB/s and writing at around 15 MB/s.

    However, the issue is that smaller files (< 1 GB or so) are copied very fast, whereas larger files (> 1 GB or so) start copying at high speed for a few seconds then drop to slow speed and take much longer to finish copying. This happens consistently on all four USB sockets with various USB drives, the only variable being the file size.

    (My anti-virus program is Microsoft Security Essentials, which took only a few seconds to scan the larger files when I checked just now, so that does not seem be the cause of their slow copying.)

    So is something wrong somewhere, or is there an inherent speed limitation somewhere when copying large files?
    Last edited by Murgatroyd; 2016-02-13 at 00:22.

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    The hardware probably can't keep up. It may be the external device or the motherboard.
    Do you have another machine / device to compare speeds?

    cheers, Paul

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    I have two identical laptops. The issue (initially fast & then slow copying of files larger than about 1 GB to USB drives) happens consistently on both laptops, on all sockets (all USB 3.0), with various USB drives. Hence I wondered whether something is wrong somewhere, or whether there is an inherent speed limitation somewhere when copying large files (i.e., does it happen for other people also).

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    ...whether there is an inherent speed limitation somewhere when copying large files...
    No, my experience is the exact opposite. Large files achieve much higher throughput on copies to or from USB devices. The difference is dramatic too, on the order of 5-10x.

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    I'm jumping in way over my head here because I don't know nearly enough to give you a good answer.

    When you copy a file, you are building a new file piece by piece on the destination drive. As it keeps appending more and more onto the file, it gets bigger and bigger. Something has to be keeping track of this and updating the NTFS index. Could that have anything to do with why large file copies slow down as they go.

    What are you using to do the copy? Is it Windows Explorer or some utility? Some utilities do some kind of validation as they go. They may also keep track of where in the file the copy is so that it can resume if it's interrupted.

    Like I said, just throwing things at the wall to see if anything sticks. No laughing allowed.
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    Sorry, I should clarify. When I said

    Large files achieve much higher throughput...
    What I meant was, if you have a fixed total quantity of data, say 1 GB. If that 1 GB consists of several, or even just one file, then the USB copy will be fast. If that 1 GB consists of thousands of small files the USB copy will be noticeably slower.

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    This is frightfully dated. When will you people discover the glories of USB 3.1?

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    Quote Originally Posted by dogberry View Post
    This is frightfully dated. When will you people discover the glories of USB 3.1?
    Why don't you enlighten us?

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    Quote Originally Posted by Erik47 View Post
    Why don't you enlighten us?
    I couldn’t resist USB 3.1, but I think I had better do what I can for the OP first.

    ‘Time remaining’ forecasts hop around like grasshoppers for me too, so I just ignore them.

    TeraCopy (free) is worth a try; I use it all the time for virtually all my transfers, but what effect it will have on your specific problem I can’t say.

    I have a two Seagate GoFlex drives that were sold as, and are, USB3. I have a USB3 stand to go with them, as well as ‘portable’ short leads. This one of those sorry cases in which the drive hardware was available for an extremely long time before there were any computers equipped with a USB3 port to accept it. Mine ran exclusively as USB2 for ages because I had no computer that had USB3. Now I do, and the increase in speed is clear.

    I did make an accidental discovery about speed. As an experiment – these things are always experiments – I partitioned one of the drives and set it up as a Windows to Go device, so I can boot into Windows using the drive and run it from the drive. It works, and it works superbly, but it only works if I use the much shorter and thicker ‘portable’ lead. It will not boot if it is in the stand with the long lead, even though it is still USB3 all the way.

    A chain is only as strong as its weakest link. Connections and connectors make a difference. End of lesson.

    I saw my first USB3.1 flash drive for sale at the local Staples shortly before my previous post, asked a few questions, and no, they don’t have any computers that will accommodate it. Just google for details – its progress may be worth tracking if you don’t want to spend a fortune on obsolescent hardware.

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