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Today I purchased a brand new backup hard drive (2tb Western Digital Elements, USB 2.0) and when I copy files to it from my laptop (Toshiba Satellite l300 with 7200rpm Western Digital Black 500GB HDD) the copy speed decreases over time.

For example, I just copied 25 GB of files to the HDD and slowly the copy speed went from ~30MB/s down to ~15MB/s. This just goes down in small increments over the duration of the file transfer.

The HDD is currently formatted as NTFS.

Here is my crystal mark results:

* MB/s = 1,000,000 byte/s [SATA/300 = 300,000,000 byte/s]

       Sequential Read :    21.475 MB/s
      Sequential Write :    20.617 MB/s
     Random Read 512KB :    18.958 MB/s
    Random Write 512KB :    19.593 MB/s
   Random Read 4KB (QD=1) :     2.718 MB/s [   663.5 IOPS]
   Random Write 4KB (QD=1) :     1.570 MB/s [   383.2 IOPS]
   Random Read 4KB (QD=32) :     1.029 MB/s [   251.3 IOPS]
  Random Write 4KB (QD=32) :     1.736 MB/s [   423.7 IOPS]

   Test : 50 MB [G: 7.1% (131.4/1863.0 GB)] (x5)
    Date : 2011/11/12 18:56:09
     OS : Windows 7 Home Premium Edition SP1 [6.1 Build 7601] (x64)
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1 Answer 1

up vote 3 down vote accepted

That's about it. The USB 2.0 connection itself is limited to maximum ~25MB/s ever. These external drives are packaged with cheap controllers. The whole process from the OS, through Motherboard chipsets, to USB, and the disk controller, and then the disk own controller is "a chain of buffers" and multiple sets of "data transfers" going on. As the disk fills up, you get around 15-20MB — the Big B, not the little b :-)

If it was an 80 Gigabyte drive your pain would end quickly, but it's 2TB and that means days.

Good for "storage", but if you want some major speed increases, then it's Firewire or USB3 or some dock that connects to PCMIA. Just be glad that it can work while you sleep.

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Bummer. Unfortunately due to the current price in hard drives it just wasn't affordable to get a usb 3 HDD. –  Sam Nov 12 '11 at 5:48
    
Just going to try it on another computer to be sure... –  Sam Nov 12 '11 at 5:53
2  
They put green type of low RPM drives in the enclosures , logically so it doesnt burn itself up, they will do ~50MB/s When on the slow end of the platters, the USB should be able to maintain ~25MB/s , so it still doesnt make enough sence, seems like they should be able to do a Full 20-22 non-stop anyway. –  Psycogeek Nov 12 '11 at 5:57
    
That is enough speed for the 2.0. Now you can't expect from a P4 processor to do the work of Core2Duo. –  avirk Nov 12 '11 at 6:04
1  
Windows 7 seems to show a faster speed for copying at the start, then drops down to a lower speed within the first minute. I don't know why. Maybe there is something that runs (or seems to run) a bit faster at the start, due to some cache or whatever. Maybe it's just a glitch in how the speed is measured. Sometimes you can get better USB speed by changing ports, cables, adding or removing a hub or whatever - trying to improve signal quality to avoid the speed dropping or lots of re-sends - but the differences are usually marginal. –  Steve314 Nov 13 '11 at 22:07

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