What is maximum SMB2 IOCTL(FSCTL_GET_SHADOW_COPY) response size.

Hemanth Thummala hemanth.thummala at gmail.com
Mon Jan 19 15:22:14 MST 2015

Thanks all for your responses.

As Stefan(metze) and Richard pointed out, this looks like SMB2.0 limitation
to me. In negotiate process, max trans size is limited to 64K if we are not
supporting large MTU or multi credits.

I have tried modifying this max trans size from 64KB to 256KB. Could see
that it negotiating 256K with client. But there is no difference in client
behavior when trying to send huge response(~90K). Not sure if this is
SMB2.0 client's limitation. Or we might need to port the multi-credits and
large MTU support to really support huge response buffer size.

If there is a clear limitation for smb2.0 protocol, we might probably need
to truncate the response to 64K.


On Mon, Jan 19, 2015 at 8:11 AM, Volker Lendecke <Volker.Lendecke at sernet.de>

> On Mon, Jan 19, 2015 at 07:31:20AM -0800, Richard Sharpe wrote:
> > I suspect that they won't be able to test with 4.1.15 easily, and it
> > could well be the limitation of 2.02 with 64kIB max PDU size.
> >
> > They might have to simply limit their max response on this IOCTL to
> 64kiB.
> Port back the SMB2 improvements of 4.0/4.1 to 3.6 then?
> Volker
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