Half the speed when copying to same drive?

My copy speeds are half the rate when I copy to the same HDD (same partition) compared to copying to a different physical drive. All partitions in my comparison are formatted with the same large cluster size and I am copying the same large files (8Gb vmware disks.) I use SuperCopier2 to copy.

Same disk average 30Mb/s
Different disk average 60Mb/s

Also, my normal USB 3.0 transfers for large files average 50-60Mb/s.

What gives?

(2 Hitachi Deskstars, 1Tb Sata II, 7200, 32m)
(Asus P8Z68-V LE mobo, AHCI)
(Win7 x64 Sp1, Compression off, Last access off. No Raid)
4 answers Last reply
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  1. Thats because you're copying to the same drive, both your reads and writes are taking place on the same drive so part of the time it's busy reading and part of the time it's busy writing. Since you're reading the same amount of data you're writing it makes sense that you would see approximately 1/2 the performance.
  2. Quote:
    What gives?

    That pesky thing called physics! :na:

    If you're copying and pasting to the same physical drive, you're using up read and write potential of that drive at the same time. But if you're going from one physical drive to another, you're allowing each drive to do 1 function (1 is reading, and the other is writing).
    A little more detailed way to explain it, data has to be copied(read) a little at a time, then stop it's reading so it can paste (write).

    Mathematical explanation - copy/paste in 1 physical drive (numbers are theoretical and pulled from your OP)
    drive can read @ 60MB/s OR write @ 60MB/s
    test is to copy/paste 30MB
    read takes 0.5sec
    write takes 0.5sec
    total time = 1sec <-- windows and other benchmark tools takes the total time to complete 30MB the task, e.g., 30MB/s

    Hope this helps clarify. :)
  3. That makes perfect sense. I don't know why it always seemed otherwise in XP for so many years.

    Often, it seems like Windows 7 physically moves a file (especially to the Recycle bin) where XP used to just rename the directory if on the same partition. I can hear the drive working away, getting itself into a sweat.

    I know that when I turned off NTFS compression things got faster. I do defragment and optimize regularly.

    Anyway, thanks!
  4. Windows will move the file if it has to move it between different partitions, if you move the file within the same partition (or rename it) it's usually only a matter of updating the file location so in those cases it should be almost instantaneous.

    Maybe you had only 1 partition when you used XP before? Or you simply had smaller files....

    If deleting files is your only issue, you can use the Shift + Del keybord shortcut to delete the file directly without going through the recycle bin.
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