[Samba] Client link utilization

Jeremy Allison jra at samba.org
Sat Feb 6 22:07:53 MST 2010

On Sat, Feb 06, 2010 at 09:26:32PM -0600, Stan Hoeppner wrote:
> Bostjan Skufca put forth on 2/6/2010 6:14 PM:
> > Hello everybody!
> > 
> > This is probably going to be a classic question but I cannot find a
> > decent answer on net.
> > 
> > I have samba server set up and the following things work flawlessly:
> > - iperf shows 92% link utilization
> > - FTP/SCP/HTTP transfers work in 10MB/s range.
> > 
> > However, when I mount samba share with linux client (mount.cifs) the
> > link utilization cannot bypass cca 33%. Transfer speeds constantly
> > stops around 3.8MB/s and will not rise above it no matter what socket
> > and locking options I use.
> > 
> > Do you have any ideas about why this is happening and/or FAQ websites
> > to point me to?
> I've had a similar thread running for a few weeks without resolution.  In my
> case I can max the wire (100FDX) at 92Mb/s to/from Win2K and WinXP clients using
> FTP, and smbclient from the server to shares on the workstations maxes the wire
> (at least GET from the workstations does).  I'm running Samba 3.2.5 on Debian
> Lenny with custom kernel
> The max smb performance I can get in a single stream to/from smbd is 65Mb/s, or
> 8.5MB/s.  I've now tested Win2K, WinXP, and smbclient on SLED 10 (can't recall
> version).  In all cases, no matter what performance settings I tweak in smb.conf
> or on the workstations, I can't get wire speed with a single SMB stream---can't
> get over 65Mb/s.
> Interestingly, two simultaneous SMB transfer streams (two Windows Explorer file
> copy operations on the same workstation) will max the wire at 92Mb/s, or 11MB/s.

Hang on a minute, I haven't been paying attention to these emails
as yet.

Am I correct in saying:

smbclient -> smbd maxes the wire.
smbclient -> WinXP maxes the wire.

But WinXP -> smbd gets 2/3 of the wire speed.

And WinXP+WinXP (two streams) -> smbd maxes the wire.

If this is the case, it's the 64k per read/write
limit plus only one outstanding packet per stream
issue with the WinXP redirector that's the issue.

smbclient sends up to maxmux outstanding packets
on read/write and keeps the pipeline full. That's
why it can max the wire.

The WinXP redirector is just not very good I'm


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