What is maximum SMB2 IOCTL(FSCTL_GET_SHADOW_COPY) response size.

Hemanth Thummala hemanth.thummala at gmail.com
Tue Jan 20 10:21:57 MST 2015

Hi Volker,

I found hard limit(512) on the number of shadow copies(MaxShadowCopies)
that windows server can keep. With 512 snapshots, IOCTL response is not
going to exceed 32K. I don't think client will behave differently in this
case even after enable or disable the large MTU support.
Please correct me if I am wrong.


On Mon, Jan 19, 2015 at 11:39 PM, Volker Lendecke <Volker.Lendecke at sernet.de
> wrote:

> On Mon, Jan 19, 2015 at 02:22:14PM -0800, Hemanth Thummala wrote:
> > 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.
> Not sure if that makes sense to test, but what happens
> with Win7->Win7 without the DisableLargeMTU setting in this
> case?
> Volker
> --
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