[Samba] No increased throughput with SMB Multichannel and two NICs

Jeremy Allison jra at samba.org
Tue Sep 6 17:39:43 UTC 2016

On Tue, Sep 06, 2016 at 03:56:14PM +0200, Daniel Vogelbacher via samba wrote:
> Am 2016-09-06 10:41, schrieb Anoop C S via samba:
> >On Sun, 2016-09-04 at 11:42 +0200, Daniel Vogelbacher via samba wrote:
> >>Hello,
> >>
> >>I'm running Samba 4.4.5 with enabled SMB Multichannel. The Linux
> >>server
> >>has two 1GBit/s NICs and for testing purposes I've shared a tmpfs
> >>mountpoint with 2GiB and ~2GiB large test-file.
> >>
> >>My Windows 10 host has one dual-port 1GBit/s NIC, and if both
> >>interfaces
> >>are enabled, Get-SmbMultichannelConnection lists active multichannel
> >>connections to my Linux SMB server.
> >>
> >>If I disable one NIC on Windows, the other NIC is used with ~1GBit/s
> >>when transferring the test-file from Linux to Windows.
> >>If I enable both NICs, instead of 2x1Gbit/s I only get ~500MBit/s per
> >>interface (but both interfaces are used).
> >>
> >>So instead of doubling the throughput, traffic is split up between
> >>two
> >>interface half by half.
> >>
> >
> >This is mostly a Windows client-controlled behavior. Refer to the
> >following reply for a thread on similar subject for more details. 
> >
> >https://lists.samba.org/archive/samba/2016-August/201841.html
> [...]AFAIK, the windows client only puts traffic on interfaces of same
> speed and quality simultaneouslt[...]
> I interpret this as "with two identical NIC-speeds at server-side
> and client-side it should result in double throughput".
> On both hosts I've 2x1GBit/s NICs and Windows uses both(!) NICs (but
> not at full speed when multichannel is enabled). So I don't think my
> problem is related to this thread, beacuse if it is, Windows would
> choose only one NIC.

What do you have set for "aio read size"/"aio write size"
in your smb.conf ?

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