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diff --git a/docs/docbook/projdoc/Speed.xml b/docs/docbook/projdoc/Speed.xml new file mode 100644 index 0000000000..987915acd2 --- /dev/null +++ b/docs/docbook/projdoc/Speed.xml @@ -0,0 +1,273 @@ +<chapter id="speed"> + +<chapterinfo> + <author> + <firstname>Paul</firstname><surname>Cochrane</surname> + <affiliation> + <orgname>Dundee Limb Fitting Centre</orgname> + <address><email>paulc@dth.scot.nhs.uk</email></address> + </affiliation> + </author> + &author.jelmer; + &author.jht; +</chapterinfo> + +<title>Samba Performance Tuning</title> + +<sect1> +<title>Comparisons</title> + +<para> +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. +</para> + +<para> +If you want to test against something like an NT or Windows for Workgroups 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. +</para> + +<para> +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 depends on your system. +</para> + +<para> +Several people have done comparisons between Samba and Novell, NFS or +Windows NT. In some cases Samba performed the best, in others the worst. I +suspect the biggest factor is not Samba versus some other system, but the +hardware and drivers used on the various systems. Given similar +hardware, Samba should certainly be competitive in speed with other +systems. +</para> + +</sect1> + +<sect1> +<title>Socket Options</title> + +<para> +There are a number of socket options that can greatly affect the +performance of a TCP-based server like Samba. +</para> + +<para> +The socket options that Samba uses are settable both on the command +line with the <option>-O</option> option, or in the &smb.conf; file. +</para> + +<para> +The <smbconfoption><name>socket options</name></smbconfoption> section of the &smb.conf; manual page describes how +to set these and gives recommendations. +</para> + +<para> +Getting the socket options correct 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. +</para> + +<para> +The socket option TCP_NODELAY is the one that seems to make the biggest single difference +for most networks. Many people report that adding +<?latex \linebreak ?><smbconfoption><name>socket options</name><value>TCP_NODELAY</value></smbconfoption> +doubles the read performance of a Samba drive. The best explanation I have seen for +this is that the Microsoft TCP/IP stack is slow in sending TCP ACKs. +</para> + +</sect1> + +<sect1> +<title>Read Size</title> + +<para> +The option <smbconfoption><name>read size</name></smbconfoption> 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. +</para> + +<para> +This overlapping works best when the speeds of disk and network access +are similar, having little effect when the speed of one is much +greater than the other. +</para> + +<para> +The default value is 16384, but little experimentation has been +done as 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. +</para> + +</sect1> + +<sect1> +<title>Max Xmit</title> + +<para> + At startup the client and server negotiate a <parameter>maximum transmit</parameter> size, +which limits the size of nearly all SMB commands. You can set the +maximum size that Samba will negotiate using the <smbconfoption><name>max xmit</name></smbconfoption> option +in &smb.conf;. Note that this is the maximum size of SMB requests that +Samba will accept, but not the maximum size that the client will accept. +The client maximum receive size is sent to Samba by the client and Samba +honors this limit. +</para> + +<para> +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. +</para> + +</sect1> + +<sect1> +<title>Log Level</title> + +<para> +If you set the log level (also known as <smbconfoption><name>debug level</name></smbconfoption>) 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 quite +expensive. +</para> +</sect1> + +<sect1> +<title>Read Raw</title> + +<para> +The <smbconfoption><name>read raw</name></smbconfoption> operation is designed to be an optimized, low-latency +file read operation. A server may choose to not support it, +however, and Samba makes support for <smbconfoption><name>read raw</name></smbconfoption> optional, with it +being enabled by default. +</para> + +<para> +In some cases clients do not handle <smbconfoption><name>read raw</name></smbconfoption> very well and actually +get lower performance using it than they get using the conventional +read operations. +</para> + +<para> +So you might like to try <smbconfoption><name>read raw</name><value>no</value></smbconfoption> and see what happens on your +network. It might lower, raise or not effect your performance. Only +testing can really tell. +</para> + +</sect1> + +<sect1> +<title>Write Raw</title> + +<para> +The <smbconfoption><name>write raw</name></smbconfoption> operation is designed to be an optimized, low-latency +file write operation. A server may choose to not support it, however, and Samba makes support for +<smbconfoption><name>write raw</name></smbconfoption> optional, with it being enabled by default. +</para> + +<para> +Some machines may find <smbconfoption><name>write raw</name></smbconfoption> slower than normal write, in which +case you may wish to change this option. +</para> + +</sect1> + +<sect1> +<title>Slow Logins</title> + +<para> +Slow logins are almost always due to the password checking time. Using +the lowest practical <smbconfoption><name>password level</name></smbconfoption> will improve things. +</para> + +</sect1> + +<sect1> +<title>Client Tuning</title> + +<para> +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. Check the sections on the various clients in +<link linkend="Other-Clients"/>. +</para> + +</sect1> + +<sect1> +<title>Samba Performance Problem Due to Changing Linux Kernel</title> + +<para> +A user wrote the following to the mailing list: +</para> + +<para> +I am running Gentoo on my server and Samba 2.2.8a. Recently +I changed kernel version from <filename>linux-2.4.19-gentoo-r10</filename> to +<filename>linux-2.4.20-wolk4.0s</filename>. And now I have a performance issue with Samba. +Many of you will probably say, <quote>Move to vanilla sources!</quote> +Well, I tried that and it didn't work. I have a 100mb LAN and two computers (Linux and +Windows 2000). The Linux server shares directories with DivX files, the client +(Windows 2000) plays them via LAN. Before when I was running the 2.4.19 kernel +everything was fine, but now movies freeze and stop. I tried moving +files between the server and Windows and it is terribly slow. +</para> + +<para> +The answer he was given is: +</para> + +<para> +Grab the mii-tool and check the duplex settings on the NIC. +My guess is that it is a link layer issue, not an application +layer problem. Also run ifconfig and verify that the framing +error, collisions, and so on, look normal for ethernet. +</para> + +</sect1> + +<sect1> +<title>Corrupt tdb Files</title> + +<para> +Our Samba PDC server has been hosting three TB of data to our 500+ users +[Windows NT/XP] for the last three years using Samba without a problem. +Today all shares went very slow. Also the main smbd kept +spawning new processes so we had 1600+ running smbd's (normally we avg. 250). +It crashed the SUN E3500 cluster twice. After a lot of searching, I +decided to <command>rm /var/locks/*.tdb</command>. Happy again. +</para> + +<para> +<emphasis>Question:</emphasis> Is there any method of keeping the *.tdb files in top condition or +how can I detect early corruption? +</para> + +<para> +<emphasis>Answer:</emphasis> Yes, run <command>tdbbackup</command> each time after stopping nmbd and before starting nmbd. +</para> + +<para> +<emphasis>Question:</emphasis> What I also would like to mention is that the service latency seems +a lot lower than before the locks cleanup. Any ideas on keeping it top notch? +</para> + +<para> +<emphasis>Answer:</emphasis> Yes. Same answer as for previous question! +</para> + +</sect1> + +</chapter> |