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 reall 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 enable 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 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.

This is disabled by default as it didn't seem to help in most systems. 
You can enable it by using "read prediction = yes". 


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". Lowering the "read size" might
also help.


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

There are a number of socket options that may affect the performance
of a TCP based server like Samba. I have not yet experimented with
these, so it is very possible that the "default" values that Samba
uses are not very good.

If you know something about TCP and are willing to experiment then
please let me know how it goes!

Look for the setsockopt() calls in server.c to see what is currently
done.


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.
