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diff --git a/docs/textdocs/Speed.txt b/docs/textdocs/Speed.txt new file mode 100644 index 00000000000..325376ac250 --- /dev/null +++ b/docs/textdocs/Speed.txt @@ -0,0 +1,341 @@ +!== +!== Speed.txt for Samba release 2.2.0-alpha3 24 Mar 2001 +!== + +Subject: Samba performance issues +============================================================================ + +This file tries to outline the ways to improve the speed of a Samba server. + +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. + + +OPLOCKS +------- + +Oplocks are the way that SMB clients get permission from a server to +locally cache file operations. If a server grants an oplock +(opportunistic lock) then the client is free to assume that it is the +only one accessing the file and it will agressively cache file +data. With some oplock types the client may even cache file open/close +operations. This can give enormous performance benefits. + +With the release of Samba 1.9.18 we now correctly support opportunistic +locks. This is turned on by default, and can be turned off on a share- +by-share basis by setting the parameter : + +oplocks = False + +We recommend that you leave oplocks on however, as current benchmark +tests with NetBench seem to give approximately a 30% improvement in +speed with them on. This is on average however, and the actual +improvement seen can be orders of magnitude greater, depending on +what the client redirector is doing. + +Previous to Samba 1.9.18 there was a 'fake oplocks' option. This +option has been left in the code for backwards compatibility reasons +but it's use is now deprecated. A short summary of what the old +code did follows. + +LEVEL2 OPLOCKS +-------------- + +With Samba 2.0.5 a new capability - level2 (read only) oplocks is +supported (although the option is off by default - see the smb.conf +man page for details). Turning on level2 oplocks (on a share-by-share basis) +by setting the parameter : + +level2 oplocks = true + +should speed concurrent access to files that are not commonly written +to, such as application serving shares (ie. shares that contain common +.EXE files - such as a Microsoft Office share) as it allows clients to +read-ahread cache copies of these files. + +Old 'fake oplocks' option - deprecated. +--------------------------------------- + +Samba can also fake oplocks, by granting a oplock whenever a client +asks for one. This is controlled using the smb.conf option "fake +oplocks". If you set "fake oplocks = yes" then you are telling the +client that it may agressively cache the file data for all opens. + +Enabling 'fake oplocks' on all read-only shares or shares that you know +will only be accessed from one client at a time you will see a big +performance improvement on many operations. If you enable this option +on shares where multiple clients may be accessing the files read-write +at the same time you can get data corruption. + +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 request 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. + + +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. + + +SHARE MODES +----------- + +Some people find that opening files is very slow. This is often +because of the "share modes" code needed to fully implement the dos +share modes stuff. You can disable this code using "share modes = +no". This will gain you a lot in opening and closing files but will +mean that (in some cases) the system won't force a second user of a +file to open the file read-only if the first has it open +read-write. For many applications that do their own locking this +doesn't matter, but for some it may. Most Windows applications +depend heavily on "share modes" working correctly and it is +recommended that the Samba share mode support be left at the +default of "on". + +The share mode code in Samba has been re-written in the 1.9.17 +release following tests with the Ziff-Davis NetBench PC Benchmarking +tool. It is now believed that Samba 1.9.17 implements share modes +similarly to Windows NT. + +NOTE: In the most recent versions of Samba there is an option to use +shared memory via mmap() to implement the share modes. This makes +things much faster. See the Makefile for how to enable this. + + +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 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. + +My own experience wth DefaultRcvWindow is that I get much better +performance with a large value (16384 or larger). Other people have +reported that anything over 3072 slows things down enourmously. One +person even reported a speed drop of a factor of 30 when he went from +3072 to 8192. I don't know why. + +It probably depends a lot on your hardware, and the type of unix box +you have at the other end of the link. + + +MY RESULTS +---------- + +Some people want to see real numbers in a document like this, so here +they are. I have a 486sx33 client running WfWg 3.11 with the 3.11b +tcp/ip stack. It has a slow IDE drive and 20Mb of ram. It has a SMC +Elite-16 ISA bus ethernet card. The only WfWg tuning I've done is to +set DefaultRcvWindow in the [MSTCP] section of system.ini to 16384. My +server is a 486dx3-66 running Linux. It also has 20Mb of ram and a SMC +Elite-16 card. You can see my server config in the examples/tridge/ +subdirectory of the distribution. + +I get 490k/s on reading a 8Mb file with copy. +I get 441k/s writing the same file to the samba server. + +Of course, there's a lot more to benchmarks than 2 raw throughput +figures, but it gives you a ballpark figure. + +I've also tested Win95 and WinNT, and found WinNT gave me the best +speed as a samba client. The fastest client of all (for me) is +smbclient running on another linux box. Maybe I'll add those results +here someday ... + + |