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

[Jeremy Allison]

On Wed, Aug 16, 2023 at 04:02:47PM +0100, Ivan Clayson via samba wrote:
>Hello,
>
>We are currently running a Linux Samba gateway with a CephFS 
>kernel-client to allow Windows 10 clients to transfer data to and from 
>our Ceph storage cluster. We have been using this in production for a 
>while now quite successfully but we are finding that our Windows 
>clients are having their rates limited to ~1 Gbps despite having 10 
>Gbit interfaces (iperf tests show a 4.18 Gbps network speed). We can 
>achieve far higher transfer rates when using Linux clients by setting 
>the "wsize" and "rsize" mount.cifs options (we find that 8MB works 
>well) but we've been unable to find an equivalent option for our 
>Windows clients as there doesn't seem to be an option to specify how 
>much the data will be sent in 1 SMB request.
>
>When inspecting the logs (as well as with Wireshark), we can see that 
>the Linux clients have their read and write data lengths specified by 
>the "wsize" and "rsize" options:

I don't know of any Windows client tuning parameter to set to
increase their r/w sizes (or even to change them in any way).

Any Windows experts on this list who might know a "secret"
registry key ?