This may not have anything to do with the OS but here are the results of copying the same 20GB file between two internal SSDs and over the network. For internal disk transfers, the peak followed by long dips seems top be a consistent pattern.

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How could I narrow down the cause of these dips?

Hardware: Core i7 3770, 32GB Ram, Intel SSD 500GB x 2 Network: Gigabit ethernet with linksys switches and cat6 cabling

1 Answer 1


Windows normally uses about half of the memory for caching disk files.

This means that when copying, Windows at first reads and writes very fast the data, but that is an illusion since the data is only copied to memory. When the memory cache is full, Windows then has to wait for some writes to the disk to physically terminate in order to liberate cache space, which is when the slow-down starts to be felt.

The copy operation at this point will be done in spurts: Reading quickly to memory, then wait, repeating itself again until the copy is finished. The displayed speed in this phase depends on the amount of memory of the computer: The more memory there is, the more visible are the spikes.

In case of network copy, as the physical write is slower and as it might take longer for full speed to be attained, there are many more variables that can affect the copy speed, pertaining to the nature of the connection.

This behavior is built-into Windows and cannot be changed. Some file-copy products claim to be able to copy faster than the Windows copy, but the ones I tried only seemed marginally faster. If you wish to try some of them, see : Best Free File Copy Utility.

To finish, here is one famous cartoon:


  • Thank you. The internal transfer patterns seems very consistent with your answer. Network copy however, is another story and like you said there may be other variables related to the LAN setup. Since most of my data resides on NAS drives, this does become an issue when transferring files. Streaming HD audio/video is no problem of course. Would you be able to point me to any resources about optimizing the network for large file transfers? Mar 11, 2014 at 12:00
  • If you can use FTP with your NAS, transfers will probably be faster (unless you are already at the limit).
    – harrymc
    Mar 11, 2014 at 14:57
  • Thanks. Will award the bounty when SO allows in a few hours I guess. Mar 11, 2014 at 16:55
  • As mentioned over Network the standard caching behavior and protocoll overhead for SMB-Transfers is not optimal - so you should use FTP or a similar protocoll. Depending on the connection quality you can tune much with the Packet-Size setting and if you're using wifi, there is a ton of settings for improving throughput.
    – Falco
    Mar 12, 2014 at 10:30

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