Chapter 39. Samba Performance Tuning

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 @@ -20,14 +20,14 @@ 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 +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 @@ -36,11 +36,11 @@ 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 +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 +

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 @@ -56,10 +56,10 @@ 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, +

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 +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 @@ -70,41 +70,41 @@ 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 +

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 +

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 +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 +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 +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 +

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 +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 +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

+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 @@ -119,7 +119,7 @@ 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. @@ -137,4 +137,4 @@ 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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