This file tries to outline the ways to improve the speed of a Samba server.

Andrew Tridgell
January 1995


COMPARISON
----------

The Samba server uses TCP to talk to the client. Thus if you are
trying to see if it performs well you should really compare it to
programs that use the same protocol. The most readily available
programs for file transfer that use TCP are ftp or another TCP based
SMB server.

If you want to test against something like a NT or WfWg server then
you will have to disable all but TCP on either the client or
server. Otherwise you may well be using a totally different protocol
(such as Netbeui) and comparisons may not be valid.

Generally you should find that Samba performs similarly to ftp at raw
transfer speed. It should perform quite a bit faster than NFS,
although this very much depends on your system.

MAX XMIT
--------

At startup the client and server negotiate a "maximum transmit" size,
which limits the size of nearly all SMB commands. You can set the
maximum size that Samba will negotiate using the "max xmit = " option
in smb.conf.

It defaults to 65536 bytes (the maximum), but it is possible that some
clients may perform better with a smaller transmit unit. Trying values
of less than 2048 is likely to cause severe problems.

In most cases the default is the best option.


READ SIZE
---------

The option "read size" affects the overlap of disk reads/writes with
network reads/writes. If the amount of data being transferred in
several of the SMB commands (currently SMBwrite, SMBwriteX and
SMBreadbraw) is larger than this value then the server begins writing
the data before it has received the whole packet from the network, or
in the case of SMBreadbraw, it begins writing to the network before
all the data has been read from disk.

This overlapping works best when the speeds of disk and network access
are similar, having very little effect when the speed of one is much
greater than the other.

The default value is 2048, but very little experimentation has been
done yet to determine the optimal value, and it is likely that the best
value will vary greatly between systems anyway. A value over 65536 is
pointless and will cause you to allocate memory unnecessarily.

Note: "read size" was first introduced in 1.8.06

LOCKING
-------

By default Samba does not implement strict locking on each read/write
call (although it did in previous versions). If you enable strict
locking (using "strict locking = yes") then you may find that you
suffer a severe performance hit on some systems.

The performance hit will probably be greater on NFS mounted
filesystems, but could be quite high even on local disks.

LOG LEVEL
---------

If you set the log level (also known as "debug level") higher than 2
then you may suffer a large drop in performance. This is because the
server flushes the log file after each operation, which can be very
expensive. 

WIDE LINKS
----------

The "wide links" option is now enabled by default, but if you disable
it (for better security) then you may suffer a performance hit in
resolving filenames. The performance loss is lessened if you have
"getwd cache = yes", which is now the default.

READ RAW
--------

The "read raw" operation is designed to be an optimised, low-latency
file read operation. A server may choose to not support it,
however. and Samba makes support for "read raw" optional, with it
being enabled by default.

In some cases clients don't handle "read raw" very well and actually
get lower performance using it than they get using the conventional
read operations. 

So you might like to try "read raw = no" and see what happens on your
network. It might lower, raise or not affect your performance. Only
testing can really tell.

READ PREDICTION
---------------

Samba can do read prediction on some of the SMB commands. Read
prediction means that Samba reads some extra data on the last file it
read while waiting for the next SMB command to arrive. It can then
respond more quickly when the next read request arrives. It will only
do this on files opened read only.

This is disabled by default. You can enable it by using "read
prediction = yes".

Note that you may find that read prediction is more successful if you
use "read raw = no" as raw reads don't use the read prediction code.
Also note that read prediction is only used on files that were opened
read only.

Read prediction should particularly help for those silly clients (such
as "Write" under NT) which do lots of very small reads on a file.

Samba will not read ahead more data than the amount specified in the
"read size" option. It always reads ahead on 1k block boundaries.


MEMORY MAPPING
--------------

Samba supports reading files via memory mapping them. One some
machines this can give a large boost to performance, on others it
makes not difference at all, and on some it may reduce performance.

To enable you you have to recompile Samba with the -DUSE_MMAP=1 option
on the FLAGS line of the Makefile.

Note that memory mapping is only used on files opened read only, and
is not used by the "read raw" operation. Thus you may find memory
mapping is more effective if you disable "read raw" using "read raw =
no".


WEIRDNESS
---------

One person has reported that setting the protocol to COREPLUS rather
than LANMAN2 gave a dramatic speed improvement (from 10k/s to 150k/s).

I suspect that his PC's (386sx16 based) were asking for more data than
they could chew. I suspect a similar speed could be had by setting
"read raw = no" and "max xmit = 2048", instead of changing the
protocol. Lowering the "read size" might also help.


SOCKET OPTIONS
--------------

There are a number of socket options that can greatly affect the
performance of a TCP based server like Samba.

The socket options that Samba uses are settable both on the command
line with the -O option, or in the smb.conf file.

The "socket options" section of the smb.conf manual page describes how
to set these and gives recommendations.

Getting the socket options right can make a big difference to your
performance, but getting them wrong can degrade it by just as
much. The correct settings are very dependent on your local network.


SLOW LOGINS
-----------

Slow logins are almost always due to the password checking time. Using
the lowest practical "password level" will improve things a lot. You
could also enable the "UFC crypt" option in the Makefile.

Samba Version 1.8.05 also had a bug in the status handling code that
caused it to produce an enourmous lock file. This slowed down logins a
lot. Using status=no or upgradiing should fix the problem.


CLIENT TUNING
-------------

Often a speed problem can be traced to the client. The client (for
example Windows for Workgroups) can often be tuned for better TCP
performance.

See your client docs for details. In particular, I have heard rumours
that the WfWg options TCPWINDOWSIZE and TCPSEGMENTSIZE can have a
large impact on performance.

Also note that some people have found that setting DefaultRcvWindow in
the [MSTCP] section of the SYSTEM.INI file under WfWg to 3072 gives a
big improvement. I don't know why.


COMMENTS
--------

If you've read this far then please give me some feedback! Which of
the above suggestions worked for you?

Mail the samba mailing list or Andrew.Tridgell@anu.edu.au
