Chapter 39. Samba Performance Tuning

Chapter 39. Samba Performance Tuning
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Paul Cochrane

Dundee Limb Fitting Centre

<paulc@dth.scot.nhs.uk>

Jelmer R. Vernooij

The Samba Team

<jelmer@samba.org>

John H. Terpstra

Samba Team

<jht@samba.org>

Table of Contents

Comparisons
Socket options
Read size
Max xmit
Log level
Read raw
Write raw
Slow Logins
Client tuning
Samba performance problem due changing kernel
Corrupt tdb Files

Comparisons

-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. -

-Several people have done comparisons between Samba and Novell, NFS or -WinNT. In some cases Samba performed the best, in others the worst. I -suspect the biggest factor is not Samba vs 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. -

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. -

-The socket option TCP_NODELAY is the one that seems to make the -biggest single difference for most networks. Many people report that -adding socket options = TCP_NODELAY 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. -

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 16384, 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. -

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. 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 -honours this limit. -

-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. -

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. -

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. -

Write raw

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

-Some machines may find write raw slower than normal write, in which -case you may wish to change this option. -

Slow Logins

-Slow logins are almost always due to the password checking time. Using -the lowest practical password level will improve things. -

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. Check the sections on the various clients in -Samba and Other Clients. -

Samba performance problem due changing kernel

-Hi everyone. I am running Gentoo on my server and samba 2.2.8a. Recently -I changed kernel version from linux-2.4.19-gentoo-r10 to -linux-2.4.20-wolk4.0s. And now I have performance issue with samba. Ok -many of you will probably say that move to vanilla sources...well I tried -it too and it didn't work. I have 100mb LAN and two computers (linux + -Windows2000). Linux server shares directory with DivX files, client -(windows2000) plays them via LAN. Before when I was running 2.4.19 kernel -everything was fine, but now movies freezes and stops...I tried moving -files between server and Windows and it's terribly slow. -

-Grab 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, etc... look normal for ethernet. -

Corrupt tdb Files

-Well today it happened, Our first major problem using samba. -Our samba PDC server has been hosting 3 TB of data to our 500+ users -[Windows NT/XP] for the last 3 years using samba, no problem. -But today all shares went SLOW; 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 rm /var/locks/*.tdb. Happy again. -

-Q1) Is there any method of keeping the *.tdb files in top condition or -how to early detect corruption? -

-A1) Yes, run tdbbackup each time after stopping nmbd and before starting nmbd. -

-Q2) What I also would like to mention is that the service latency seems -a lot lower then before the locks cleanup, any ideas on keeping it top notch? -

-A2) Yes! Same answer as for Q1! -

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