[Samba] SMB/CIFS seq. transfers top out at 30MiB/s (NFSv4 and HTTP: 100MiB/s+)

[Johannes Truschnigg]

Hello list,

I'm using Samba 3.4.5 on a home-hosted fileserver of mine to easily share 
files with both GNU/Linux and Windows XP (Professional 32Bit SP3) clients. The 
machines are connected to each other via a switched GBit ethernet network, the 
actual available bandwidth between the server and the nodes over TCP amounts 
to about 940-980MBit (according to iperf).

The server's storage backend is aquite potent, and achieves sequential read 
and write speeds well over the network's linespeed (somewhere around 180MiB/s 
read and 130MiB/s write at worst and well over 200MiB/s and 160MiB/s, resp., 
at best). When serving files from the very same filesystem as with Samba, 
Apache 2.2 delivers about 110MiB/s on average, and NFSv4-transfers match that 
number in terms of speed.

With Samba and SMB/CIFS, however, the transfer speed tops out at rather 
disappointing 28-30MiB/s, serving both Windows and GNU/Linux clients. I'm 
using the in-kernel CIFS support on the GNU/Linux machines, and the default 
"Attach Network Drive"-feature with Windows. Using the (afaik pure userspace) 
`smbclient` implementation on the GNU machine doesn't change anything to the 
better, the speed remains at the aforementioned ~30MiB/s.

The server system isn't really loaded while serving files over CIFS (its cores 
don't even clock to higher frequencies, but remain at a comfortable 1GHz), and 
smbd never consumes substantially more than ~15% CPUtime while reading from 
disk and delivering to the clients.

I tried adopting advice from the Samba manual's performance tuning section 
(http://www.samba.org/samba/docs/man/Samba-HOWTO-Collection/speed.html), but 
that didn't improve the situation at all - transfer speed remained roughly the 
same, compared to these settings' default values. Playing with the clients' 
mount options (rsize and wsize, specifically) didn't yield any noticeable 
improvements, either.

I continue to see other peoples' reports on the web that they manage to 
squeeze much higher transfer rates (70MiB/s+) out of dedicated NAS appliances 
via SMB/CIFS (most of which supposedly also run Samba for providing that 
service), and I fail to see why my platform won't deliver similar results, as 
the hardware should easily match whatever those NAS-devices offer.

Below I will list what I think might be relevant information to track down 
what's wrong; in case I'm missing something that'd be of use, please, let me 
know!

----SNIP START: egrep -v '^[[:space:]]*[;#]|^$' /etc/samba/smb.conf ----
[global]
    workgroup = ARBEITSGRUPPE
    security = share
    load printers = no
    guest account = nobody
    dns proxy = no
    syslog = 1
    syslog only = yes
    socket options = SO_RCVBUF=8192 SO_SNDBUF=8192
    disable netbios = yes
    unix extensions = yes
    unix charset = UTF-8
    display charset = UTF-8
    use mmap = yes
    use sendfile = yes
    wins support = no
[files]
   path = /srv/files/pub/
   public = yes
   only guest = yes
   writable = yes
   printable = no
---- SNIP END: egrep -v '^[[:space:]]*[;#]|^$' /etc/samba/smb.conf ----

My GNU/Linux client mounts the share with the following options:
---- SNIP START: /etc/fstab ----
//virtue.local/files /media/network cifs \ 
auto,user,pass=,rw,uid=1000,gid=100,noexec,nolock,\
file_mode=0664,dir_mode=0775,iocharset=utf8,\
wsize=57344,rsize=57344 0 0
---- SNIP END: /etc/fstab ----

The output of `smbd -d` is recorded here: http://pasted.at/fb1889588d_nl.html

All GNU/Linux clients use recent (2.6.32+) kernels and are x86_64 machines. 
All clients are able to get the HTTP transfer speeds described above.

I'm still using the very same kernel that was used to build Samba/smbd on. 
There's nothing out of the ordinary recorded in the server's logs.  `nmbd` 
isn't running on the server, as I don't need that kind of name resolution 
support. Samba is Version 3.4.5, running on Gentoo GNU/Linux ~amd64.


If anyone spots something obvious that might limit transfer speeds in the way 
I described, please leave a comment. Thanks very much in advance for your time 
and effort!
-- 
with best regards:
- Johannes Truschnigg ( johannes at truschnigg.info )

www: http://johannes.truschnigg.info/
phone: +43 650 2 133337
xmpp: johannes at truschnigg.info

Please do not bother me with HTML-eMail or attachments. Thank you.
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