[cifs-protocol] [REG: 116022313745563] Windows 10 backup failing against Samba

Kamil Sykora kamils at microsoft.com
Tue Feb 23 20:44:04 UTC 2016

[BCC: dochelp, CC: casemail]

Hello Uri,

Thank you for contacting the Open Specifications support team. I have created incident 116022313745563 to track your issue. One of our engineers will contact you shortly to start working with you.


Kamil Sykora 
tel. (980) 776-7508 
working hours 8:00 a.m.- 5:00 p.m. EST, Mon-Fri 
manager name: Nam Su Kang nkang at microsoft.com 
kamils at microsoft.com

-----Original Message-----
From: Uri Simchoni [mailto:uri at samba.org] 
Sent: Tuesday, February 23, 2016 3:05 PM
To: Bryan Burgin <bburgin at microsoft.com>; Interoperability Documentation Help <dochelp at exchange.microsoft.com>
Cc: cifs-protocol at lists.samba.org
Subject: Windows 10 backup failing against Samba

Hi Bryan,

Continuing the discussion from samba-technical.

We have a Windows 10 VM (details attached) failing to create a system image on a Samba 4.3.4 server share. We would like to understand the root cause so that a fix can be supplied.

To reproduce:
1. Setup a stand-alone Samba-based file server as per https://wiki.samba.org/index.php/Standalone_server

(I basically used the Fedore FC23 build, with a minimal smb.conf as listed in the wiki, and an ext4 file system. had do disable selinux to avoid frustration. But it should behave the same on other builds)

2. On a Win10 machine, create a system image using wbadmin command line, as listed in attached cmd.txt session

After snapshot creation phase, the operation fails with "incorrect function" error message.

info.txt - basic details on the client OS cmd.txt - capture of the wbadmin command and output backup.pcap - packet capture of the SMB3 session

The packet capture shows an attempt to open the .vhdx with SVHDX_OPEN_DEVICE_CONTEXT, which returns this error.

If my reading of [MS-SMB2] is correct, then Samba is in compliance here, since it does not support shared VHDX.

It's not entirely clear how/whether the client is supposed to test for support of SVHDX - I'm waiting to get my hands on a Server
2012R2/2016TP4 to compare. In an SDC presentation from 2013 it says the existence of an alternate data stream is the test, I see no such test in the packet capture.

Please advise.


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