windows 2000: slow file copy from windows 2000 to SAMBA

Jeremy Allison jeremy at
Wed May 23 16:58:13 GMT 2001

"Coupal, Chris ISC" wrote:
> Greetings,
> I have a interesting problem copying large files from a Windows2000 server
> to a SAMBA share. The copy takes extremely long. For example, a 600K file
> takes in excess of 40 seconds. Initially, we had the problem copy the file
> to NT 4 machines as well, but we fixed it with the following work around
> which explains the problem well:
> Is there a way we can apply the same "FIX" to samba?

You, sir, are a hero ! I looked at those msdn entries...

It turns out the we didn't understand the implications of

NT normally negotiates a small (4k) buffer, and so sends
very small read/write requests. It uses raw reads/writes
to send larger reads and writes, *BUT ONLY UP TO THE 64k

This is a very important thing. Samba *always* offers a
64k buffer size to the client, so there really is no difference
for us between raw and normal reads/writes.

Microsoft "LARGE" read and writes have the capability
to be 32 bit (if you look at the CIFS spec) as they
dedicate a new 16 bit length field on top of the existing
one. However, the NetBIOS frame size prohibits this from
actually being used, so on the wire their "large" read/writes
are just 0xF000 (for safety I guess). Samba can *already*
handle reads and writes of this size as we allocate a
64k buffer anyway.

So..... it turns out all you need to do is apply the
following patch (which I've just applied to the 2.2 and HEAD
sources) - and W2K clients are very fast indeed with a
Samba server :-) :-). It's very simple as all we're doing
is telling W2k clients  "hey, we *already* support your large
read/writes" - which we do !

Thanks a *lot* for making me spend the time to look at


Index: include/smb.h
RCS file: /data/cvs/samba/source/include/smb.h,v
retrieving revision 1.325.2.24
diff -u -r1.325.2.24 smb.h
--- include/smb.h       18 May 2001 20:16:57 -0000      1.325.2.24
+++ include/smb.h       23 May 2001 18:44:43 -0000
@@ -1417,6 +1417,7 @@
 #define CAP_NT_FIND          0x0200
 #define CAP_DFS              0x1000
 #define CAP_LARGE_READX      0x4000
+#define CAP_LARGE_WRITEX        0x8000
 #define CAP_EXTENDED_SECURITY 0x80000000

 /* protocol types. It assumes that higher protocols include lower protocols
Index: smbd/negprot.c
RCS file: /data/cvs/samba/source/smbd/negprot.c,v
retrieving revision
diff -u -r1.16.4.5 negprot.c
--- smbd/negprot.c      8 Mar 2001 14:49:28 -0000
+++ smbd/negprot.c      23 May 2001 18:44:44 -0000
@@ -160,6 +160,9 @@
   /* dual names + lock_and_read + nt SMBs + remote API calls */
                      (lp_nt_smb_support() ? CAP_NT_SMBS |
+#if 1 /* JRATEST */
+                                        CAP_LARGE_READX | CAP_LARGE_WRITEX
                      (SMB_OFF_T_BITS == 64 ? CAP_LARGE_FILES : 0);

Buying an operating system without source is like buying
a self-assembly Space Shuttle with no instructions.

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