copy offload for SMB?

David Disseldorp ddiss at
Fri Feb 22 08:08:50 MST 2013

Hi Richard,

On Fri, 22 Feb 2013 06:45:36 -0800
Richard Sharpe <realrichardsharpe at> wrote:

> On Fri, Feb 22, 2013 at 2:30 AM, David Disseldorp <ddiss at> wrote:
> > On Thu, 21 Feb 2013 21:49:35 -0800
> > Richard Sharpe <realrichardsharpe at> wrote:
> >> Now to check if W2K08 sends such an FSCTL to see if it can get a resume key.
> >
> > 2k8 doesn't use it for copies initiated via Explorer, 2k12 does though.
> > See source3/smbd/smb2_ioctl_network_fs.c for the Samba implementation.
> Thanks. Do you know if it is exposed on W2K08 via CopyFileEx or
> something like that?

Server support is there, with a few quirks[1]. I'm not aware of anything
pre-2k12 that uses it on the client side, but the ioctl itself has been
around for donkey's years (SMB1), so there's likely something obscure
using it.

Cheers, David

1. [cifs-protocol] FSCTL_SRV_COPYCHUNK locking discrepancies

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