We have a 10 Gigabit network with a mix of Windows 10, Linux and MacOS (Sierra 10.12.6) machines.

The transfer speeds between the Windows or Linux machines are OK: between 500 and 800 MB/s for big files (10 to 100 GB).

But the Macs show a read speed of around 130 MB/s only.

Curiously, write speeds when writing from Mac to Windows or Linux, are much better. The slow speed is when transferring files between two Macs or when the Mac is reading from a Win/Linux share.

The problem is really specific to SMB on Mac.

  • All the machines have SMB signing disabled as per Apple's recommendation. With the default setting which enables signing, the speeds were even (a lot) worse: around 60-70 MB/s.

  • The disks used were all RAID 5 arrays with local speeds between 600 MB/s. and over 1 GB/s. (tested with dd and Blackmagic Speed Test)

  • The raw network speeds tested with iperf3 were between 5 and 10 Gigabits/s.
  • Using FTP instead of SMB showed speeds around 500 MB/s in both directions (using the Mac's default ftpd).

Other suggestions I came across, which of course made no difference:

  • Using IP addresses instead of hostnames.
  • Using cifs:// instead of smb://. (that acually forces SMB 1 instead of SMB 3, and made the speed much worse)
  • What version of Samba are you running on your server? – user260467 Jan 21 at 14:43
  • Is there any way for you to test a High Sierra or Mojave client? – user260467 Jan 21 at 14:43
  • @user260467 : The Macs are not using Samba, but Apple's own SMB implementation, that comes with OS 10.12.6. The servers were a Win10 (v 1807) machine and a CentOS 7 with Samba 4.7.1. Unfortunately, I can not try other Mac versions now. There might be a notebook with a higher MacOS version, but without 10G, and without fast enough disks anyway. – mivk Jan 22 at 21:47

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