Need explanation on odd figures from Copy/Transfer rates  

  1. Posts : 1,290
    Windows 10

    Need explanation on odd figures from Copy/Transfer rates


    So basically the issue (You can read in details bellow) was that on copying files one gets three different readings , Explorer report a figure between 35 ~ 70 MB/s , Task Manager Disk % Transfer Rate reports double the number & yet Disk % Utilization never exceeds 50~60% .

    Thanks to @dalchina & @Samuria I was able to experiment with the issue a little more and here are my findings :

    1 - Apparently on file Copy windows deal with Explorer as yet another program running with Normal priority assigning to it a Quota of Disk % Utilization (a Cap) where Explorer as a program do the Reading then hands it in a Queue like action to the System Process to do the Writing , so Explorer just report its part (the Reading speed in MB/s) and yet Disk % Transfer rate combines it along with the Writing done by the System as well :
    Need explanation on odd figures from Copy/Transfer rates-rm1.jpg

    2 - The reason of priority and capping was revealed to me as on conducting the same experiment with Robocopy (A fast folder copy command line tool suggested by Samuria) , when the system reached its Disk % Utilization peek (95~100%) the system starts becoming slightly unresponsive .

    3 - Now on the other hand Robocopy command despite not running in any higher priority somehow trigger the System to assist it in Reading so the Cap limiting is off (i.e the System Read along with it at the exact capped speed) to render a full Disk % Utilization :
    Need explanation on odd figures from Copy/Transfer rates-rm2.jpg

    4 - There are few side effects to Robocopy other than System responsiveness and those are :
    a - The documentation is Jerky
    b - You can't monitor progress or have an estimate on when it's done
    c - It uses an odd method of committing all files in last step
    (i.e you wont be seeing a single file output until it is done copying/moving all)
    d - It is designed for directory copy , no file copy support

    5 - Microsoft made a GUI for Robocopy as it is essentially a command line tool which is difficult to find so I have included it in post attachments yet however it only ease up using it but wouldn't solve the no progress monitor or time estimate or pause or cancel problem etc .


    --Original Post--
    Ok so basically I am trying to figure why would I get 3 different readings from windows from a file Copy/Move operation , first things first this is an internal SSHD trying to copy files to another internal SSHD both running on a Sata 3 interface .

    Now the remark is I get a fluctuating rate between 70 ~ 35 MB/s reported on Copy/Transfer Dialogue and then exactly double the figure on Task Manager "Disk % Transfer Rate" and Yet less than 50% Cap to "Disk % Utilization" .

    Need explanation on odd figures from Copy/Transfer rates-sshd.jpg

    Now Maybe but not really sure I can assume that the "Disk % Transfer Rate" doubles figures to portray cumulative disk utilization of both disks . Now why is it still capped under 50% if the Sata interface can take it ? Defragmantation ? Can defragmentation cause a 50% cap ?

    Which lead me to try it but this time to a USB 3 external HDD and here are the results :

    Need explanation on odd figures from Copy/Transfer rates-sshd2.jpg

    Again the numbers are doubled in "Disk % Transfer Rate" and while the transfer rate is higher the "Disk % Utilization" is lower , so can anyone confirm why these numbers are all messed up like that ?
    Need explanation on odd figures from Copy/Transfer rates Attached Files
    Last edited by nIGHTmAYOR; 15 Oct 2018 at 12:54.
      My Computer

  2. Posts : 40,533
    Win 10 Pro (22H2) (2nd PC is 22H2)

    Hi, if you look at your Resource Monitor with activity on 1 physical disk only, you should be able to work out what means what:

    Need explanation on odd figures from Copy/Transfer rates-1.jpg

    There you can see read, write, and total.

    Also see the disk transfer rate under the Performance tab.
      My Computers

  3. Posts : 7,750
    windows 10

    Many things effect the transfer speed CPU usage even loading taskmaster can effect it. Often anti virus will slow it to a crawl as it scans files on read and right the fastest is to use built in robocopy as it has no overhead and designed for this job
      My Computer

  4. Posts : 5,478

    Your fiirst example is write speed 47, total disk 88. Your second is write speed 56, total 112.

    In both cases the write speed is almost exactly half the total disk I/O. In fact your second example is much cleaner - it has reached a consistent write speed and there is no point in your internal disk trying to push more at it as the write limit is reached.

    As you need to read and write it makes sense that other things being equal and no bottlenecking occurs elsewhere the total disk I/O is half the write speed.

    The utilisation % in Windows is almost completely useless as a statistic as far as I understand it (I am not an expert here though). It means what percentage of the time the disk is in use rather than having anything at all to do with transfer rates. I'm not sure really why it is even shown as you can easliy end up with 100% utilisation by time and 0.1MB/s transfer rates. This is often reported as a bug but really isn't.
      My Computer

  5. Posts : 1,290
    Windows 10
    Thread Starter

    Thank you guys , been a great help , I wrapped up my findings to the benefit of whomever that reads it .
      My Computer


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