What is maximum SMB2 IOCTL(FSCTL_GET_SHADOW_COPY) response size.

Hemanth Thummala hemanth.thummala at gmail.com
Sun Jan 18 22:55:47 MST 2015


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

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.


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