This file tries to outline the ways to improve the speed of a Samba server. Andrew Tridgell January 1995 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. 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. 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. 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. 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. You can enable it by using "read prediction = yes". 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". SLOW CLIENTS ------------ 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. 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. 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