What is maximum SMB2 IOCTL(FSCTL_GET_SHADOW_COPY) response size.

Stefan (metze) Metzmacher metze at samba.org
Mon Jan 19 00:41:45 MST 2015

Am 19.01.2015 um 08:27 schrieb Jeremy Allison:
> On Sun, Jan 18, 2015 at 09:55:47PM -0800, Hemanth Thummala wrote:
>> Hi,
>> We are using samba 3.6.12+ stack. We are implemented windows previous
>> version(shadow copies) support with new VFS module.
>> On one of our nodes, there are huge number(~2K) of snapshots and we trying
>> to send them(as list) as part of IOCTL response for FSCTL_GET_SHADOW_COPY.
>> Response size is coming around 90K. Client is facing an issue in receiving
>> the huge response packet. After receiving around 65K data( calculated
>> acknowledged TCP segments), client returning TCP zero size recv window
>> error followed by connection reset. Client behavior is same irrespective of
>> version. I have tested on win 7, windows 8 and win2K12 server.
>> Would like to know if there is any limit on this IOCTL response. Client
>> negotiated 64K as max transaction size but this is the request buffer size
>> that server can accept. Did not find any documentation about SMB2 client
>> limits.
>> We couldn't verify this against windows as windows supports only 512 VSS
>> copies in back end. So it will never need to send more than 512 snapshots
>> to client.
> Sounds like you're hitting the trans2 limit on SMB1.
> That limit is 1MB on SMB2 so it should work there.

It's 64k with SMB 2.02 or without multi-credit support on the transport.

Can you also test with 4.1.15 and check if it happens there too?
Please test "server max protocol = SMB2_02" as well as the default.


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