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

[Jones Syue 薛懷宗]

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

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Regards,
Jones Syue | 薛懷宗
QNAP Systems, Inc.