I just got a new external USB 3.0 HDD (Seagate Expansion 6TB), formatted as NTFS. When writing large files to that HDD via the Windows 7 Professional explorer, I see very slow writing speeds according to the Windows copy "speed-o-meter" (around 32MB/s). Reading speeds (also using MS explorer) are much faster at around 97MB/s (so we can rule out that the drive is just running on USB 2).

Still there seems to be something wrong, and I wanted to compare benchmark speed numbers from the web (which say that an HDD should reach between 100 and 200MB/s) with mine. I used CrystalDiskMark 6.0 to get benchmark speed numbers. And here, in the "sequential" task I get speeds of 162MB/s read and 145MB/s write with my new HDD.

I can also rule out that the internal disk I am copying from is the bottleneck. According to the benchmark it can read at least 120MB/s.

So where does this large difference come from? Why can I not write in everyday normal file copying with similar speeds as in the benchmark?

Is it just that the Windows explorer is terrible at writing files at reasonable speeds? Or is it because the benchmark files are somehow simpler than the files in everyday use, so one typically does not reach benchmark speeds? In any case: How can I get closer to benchmark speeds when copying my files?


  • What is the format of the external disk - ExFAT or NTFS? – Eugen Rieck Dec 2 '18 at 11:48
  • It's formatted as NTFS. – Nameless Dec 2 '18 at 11:50
  • Copy via Windows Explorer is very slow. To achieve maximum speed try FastCopy. – harrymc Dec 2 '18 at 12:24

I found the answer: It's because I am trying to copy from a relatively old internal HDD, which can read up to 120MB/s in the sequential benchmark but is extremely slow reading smaller files (~1MB/s read in benchmark). I am guessing due to fragmentation etc the internal HDD is the bottleneck.

If I use my internal SSD to copy from, then I actually get very fast speeds with the new external HDD.

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