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

Daniel Vogelbacher daniel at vogelbacher.name
Tue Sep 6 17:58:27 UTC 2016

On 06.09.2016 19:39, Jeremy Allison via samba wrote:
> 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 ?

I don't have these options in my smb.conf.
Do you recommend any specific values?

Daniel Vogelbacher

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