[Samba] Increase data length for SMB2 write and read requests for Windows 10 clients

Jeremy Allison jra at samba.org
Tue Aug 22 16:02:20 UTC 2023

On Tue, Aug 22, 2023 at 08:50:03AM +0200, Ralph Boehme wrote:
>On 8/21/23 22:55, Jeremy Allison wrote:
>>On Mon, Aug 21, 2023 at 03:19:59PM +0200, Ralph Boehme wrote:
>>>On 8/21/23 11:53, Jones Syue 薛懷宗 via samba wrote:
>>>>>OH - that's *really* interesting ! I wonder how it is
>>>>>changing the SMB3+ redirector to do this ?
>>>>It looks like applications could do something and give a hint to SMB3+
>>>>redirector, so far not quite sure how to make it,
>>>>per process monitor (procmon) could show that write I/O size seems
>>>>could be pass from the application layers,
>>>well, sure, the application layer drives IO with the IO size it 
>>>chooses. But when the application layer issues IOs larger then the 
>>>maximum IO size allowed by SMB (8 MB iirc), the Windows SMB kernel 
>>>client will segment the larger application segments into smaller 
>>Fastcopy is doing *something* weird :-).
>>1. FastCopy (FastCopy.exe), 8MB (need to revise FastCopy default setup)
>>Process Name    Operation       Path    Detail
>>System  TCP Send ->    
>>Length: 8388724, startime: 3459115, endtime: 3459149, seqnum: 0, 
>>connid: 0
>>System  TCP Receive ->    
>>Length: 84, seqnum: 0, connid: 0
>>FastCopy.exe    WriteFile       \\\Public\1GB.img   
>>Offset: 92,274,688, Length: 8,388,608, Priority: Normal
>>I wonder if it has it's own SMB client code
>>built in ?
>>Either that or it knows what parameters to change
>>in the SMB redirector to request 8MB IO.
>I don't get it. Iirc 8 MB is the default max io size the kernel client 
>will use which is also, iirc, the limit of the protocol.

Don't get what ? The FastCopy.exe above is using 8MB write sizes.

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