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

[Jeremy Allison]

On Fri, Aug 18, 2023 at 04:25:28PM +0000, Jones Syue 薛懷宗 wrote:
>Hello Ivan,
>
>'FastCopy' has an option to revise max I/O size and works for SMB :)
>it is a tool for file transferring and could be installed to win10,
>download here: https://fastcopy.jp/
>
>This is an example for writing, a job would write a file named '1GB.img'
>from a local disk 'H:' to a remote SMB mounted net disk 'Z:',
>open 'FastCopy' tool and specify several options like:
>1. specify 'Source':  H:\1GB.img
>2. specify 'DestDir': Z:\
>3. go to Option > Main Settings > I/O Setting > I/O unit (MB),
>the default value is '1' and changes it to '8'.
>4. click button 'Execute' to start file transferring.
>
>Then we could see logs said that write size is 8MB (8388608):
>[2023/08/18 23:32:02.418926,  3] ../../source3/smbd/smb2_write.c:219(smb2_write_complete_internal)
>  smb2: fnum 4162336292, file 1GB.img, length=8388608 offset=226492416 wrote=8388608
>And wireshark said that write size is 8MB (8388608):
>SMB2	23414	Write Request Len:8388608 Off:100663296 File: 1GB.img
>
>Another example for reading, just switch the disk letter between Source
>and DestDir:
>1. specify 'Source':  Z:\1GB.img
>2. specify 'DestDir': H:\
>3. click button 'Execute' to start file transferring.
>
>And wireshark said that read size is 8MB (8388608):
>SMB2	171	Read Request Len:8388608 Off:260046848 File: 1GB.img

OH - that's *really* interesting ! I wonder how it is
changing the SMB3+ redirector to do this ?