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I have a WD My Cloud NAS. File download speed from NAS via SMB is like 20 MB/s on Windows XP and 40 MB/s on Windows 7 on the same PC. Why?

Windows 7

Copy speed: 45-53 MB/s

NAS cpu load (smbd, from top): 50-60%

Windows XP

Copy speed: 22 MB/s

NAS cpu load (smbd, from top): 26-28%

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Because Windows XP uses SMB1, which isn’t all that great. Windows 7, on the other hand, uses SMB2, which is quite an improvement.

The CPU of your NAS is the limiting factor here. SMB2 is much more efficient, thus allowing for higher transfer rates.

Microsoft has a Technet blog article on that, containing this picture:

enter image description here

The first spike is an SMB2 transfer, while the much slower transfer is done using SMB1.

Of course, Wikipedia also has an article on SMB.

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  • I doubt that since CPU load on the NAS with Windows XP is under 30%
    – Smit Johnth
    Apr 18, 2018 at 20:13
  • Looking at the load average doesn’t really tell you what’s limiting. I may have worded it badly/wrong, but with SMB1 the CPU is of course mostly idle because the whole transfer involves a lot of (slow) roundtrips over the network. With SMB2, you should see much higher CPU load. Of course, it may still use only one core.
    – Daniel B
    Apr 18, 2018 at 20:18
  • I'm pretty sure if the CPU was the bottleneck I would see constant 100% CPU load. See also what I've wrote about iperf.
    – Smit Johnth
    Apr 18, 2018 at 20:20
  • Not necessarily. It's mostly I/O, after all. iperf isn't Samba and cannot be used to measure or predict Samba performance. Like I wrote: It's SMB1 vs SMB2. // edit: Or are you perhaps saying that iperf is also slower on XP?
    – Daniel B
    Apr 18, 2018 at 21:59
  • Haven't measured it with iperf under Win7, but it's slower as SMB file transfer under Win7. And I'm sorry, but I don't think that CPU requirements matter if you have CPU usage at ca. 30%.
    – Smit Johnth
    Apr 18, 2018 at 23:55

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