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  • Improving TCP performance over a gigabit network with lots of connections and high traffic of small packets

    - by MinimeDJ
    I’m trying to improve my TCP throughput over a “gigabit network with lots of connections and high traffic of small packets”. My server OS is Ubuntu 11.10 Server 64bit. There are about 50.000 (and growing) clients connected to my server through TCP Sockets (all on the same port). 95% of of my packets have size of 1-150 bytes (TCP header and payload). The rest 5% vary from 150 up to 4096+ bytes. With the config below my server can handle traffic up to 30 Mbps (full duplex). Can you please advice best practice to tune OS for my needs? My /etc/sysctl.cong looks like this: kernel.pid_max = 1000000 net.ipv4.ip_local_port_range = 2500 65000 fs.file-max = 1000000 # net.core.netdev_max_backlog=3000 net.ipv4.tcp_sack=0 # net.core.rmem_max = 16777216 net.core.wmem_max = 16777216 net.core.somaxconn = 2048 # net.ipv4.tcp_rmem = 4096 87380 16777216 net.ipv4.tcp_wmem = 4096 65536 16777216 # net.ipv4.tcp_synack_retries = 2 net.ipv4.tcp_syncookies = 1 net.ipv4.tcp_mem = 50576 64768 98152 # net.core.wmem_default = 65536 net.core.rmem_default = 65536 net.ipv4.tcp_window_scaling=1 # net.ipv4.tcp_mem= 98304 131072 196608 # net.ipv4.tcp_timestamps = 0 net.ipv4.tcp_rfc1337 = 1 net.ipv4.ip_forward = 0 net.ipv4.tcp_congestion_control=cubic net.ipv4.tcp_tw_recycle = 0 net.ipv4.tcp_tw_reuse = 0 # net.ipv4.tcp_orphan_retries = 1 net.ipv4.tcp_fin_timeout = 25 net.ipv4.tcp_max_orphans = 8192 Here are my limits: $ ulimit -a core file size (blocks, -c) 0 data seg size (kbytes, -d) unlimited scheduling priority (-e) 0 file size (blocks, -f) unlimited pending signals (-i) 193045 max locked memory (kbytes, -l) 64 max memory size (kbytes, -m) unlimited open files (-n) 1000000 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 real-time priority (-r) 0 stack size (kbytes, -s) 8192 cpu time (seconds, -t) unlimited max user processes (-u) 1000000 [ADDED] My NICs are the following: $ dmesg | grep Broad [ 2.473081] Broadcom NetXtreme II 5771x 10Gigabit Ethernet Driver bnx2x 1.62.12-0 (2011/03/20) [ 2.477808] bnx2x 0000:02:00.0: eth0: Broadcom NetXtreme II BCM57711E XGb (A0) PCI-E x4 5GHz (Gen2) found at mem fb000000, IRQ 28, node addr d8:d3:85:bd:23:08 [ 2.482556] bnx2x 0000:02:00.1: eth1: Broadcom NetXtreme II BCM57711E XGb (A0) PCI-E x4 5GHz (Gen2) found at mem fa000000, IRQ 40, node addr d8:d3:85:bd:23:0c [ADDED 2] ethtool -k eth0 Offload parameters for eth0: rx-checksumming: on tx-checksumming: on scatter-gather: on tcp-segmentation-offload: on udp-fragmentation-offload: off generic-segmentation-offload: on generic-receive-offload: on large-receive-offload: on rx-vlan-offload: on tx-vlan-offload: on ntuple-filters: off receive-hashing: off [ADDED 3] sudo ethtool -S eth0|grep -vw 0 NIC statistics: [1]: rx_bytes: 17521104292 [1]: rx_ucast_packets: 118326392 [1]: tx_bytes: 35351475694 [1]: tx_ucast_packets: 191723897 [2]: rx_bytes: 16569945203 [2]: rx_ucast_packets: 114055437 [2]: tx_bytes: 36748975961 [2]: tx_ucast_packets: 194800859 [3]: rx_bytes: 16222309010 [3]: rx_ucast_packets: 109397802 [3]: tx_bytes: 36034786682 [3]: tx_ucast_packets: 198238209 [4]: rx_bytes: 14884911384 [4]: rx_ucast_packets: 104081414 [4]: rx_discards: 5828 [4]: rx_csum_offload_errors: 1 [4]: tx_bytes: 35663361789 [4]: tx_ucast_packets: 194024824 [5]: rx_bytes: 16465075461 [5]: rx_ucast_packets: 110637200 [5]: tx_bytes: 43720432434 [5]: tx_ucast_packets: 202041894 [6]: rx_bytes: 16788706505 [6]: rx_ucast_packets: 113123182 [6]: tx_bytes: 38443961940 [6]: tx_ucast_packets: 202415075 [7]: rx_bytes: 16287423304 [7]: rx_ucast_packets: 110369475 [7]: rx_csum_offload_errors: 1 [7]: tx_bytes: 35104168638 [7]: tx_ucast_packets: 184905201 [8]: rx_bytes: 12689721791 [8]: rx_ucast_packets: 87616037 [8]: rx_discards: 2638 [8]: tx_bytes: 36133395431 [8]: tx_ucast_packets: 196547264 [9]: rx_bytes: 15007548011 [9]: rx_ucast_packets: 98183525 [9]: rx_csum_offload_errors: 1 [9]: tx_bytes: 34871314517 [9]: tx_ucast_packets: 188532637 [9]: tx_mcast_packets: 12 [10]: rx_bytes: 12112044826 [10]: rx_ucast_packets: 84335465 [10]: rx_discards: 2494 [10]: tx_bytes: 36562151913 [10]: tx_ucast_packets: 195658548 [11]: rx_bytes: 12873153712 [11]: rx_ucast_packets: 89305791 [11]: rx_discards: 2990 [11]: tx_bytes: 36348541675 [11]: tx_ucast_packets: 194155226 [12]: rx_bytes: 12768100958 [12]: rx_ucast_packets: 89350917 [12]: rx_discards: 2667 [12]: tx_bytes: 35730240389 [12]: tx_ucast_packets: 192254480 [13]: rx_bytes: 14533227468 [13]: rx_ucast_packets: 98139795 [13]: tx_bytes: 35954232494 [13]: tx_ucast_packets: 194573612 [13]: tx_bcast_packets: 2 [14]: rx_bytes: 13258647069 [14]: rx_ucast_packets: 92856762 [14]: rx_discards: 3509 [14]: rx_csum_offload_errors: 1 [14]: tx_bytes: 35663586641 [14]: tx_ucast_packets: 189661305 rx_bytes: 226125043936 rx_ucast_packets: 1536428109 rx_bcast_packets: 351 rx_discards: 20126 rx_filtered_packets: 8694 rx_csum_offload_errors: 11 tx_bytes: 548442367057 tx_ucast_packets: 2915571846 tx_mcast_packets: 12 tx_bcast_packets: 2 tx_64_byte_packets: 35417154 tx_65_to_127_byte_packets: 2006984660 tx_128_to_255_byte_packets: 373733514 tx_256_to_511_byte_packets: 378121090 tx_512_to_1023_byte_packets: 77643490 tx_1024_to_1522_byte_packets: 43669214 tx_pause_frames: 228 Some info about SACK: When to turn TCP SACK off?

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  • Performance difference between MacBook Pro (2.8 GHz) vs Air (1.7 GHz)?

    - by jonathanconway
    I'm comparing these two Apple laptops: MacBook Pro (13", 2011 model): 2.8GHz dual-core Intel Core i7 processor with 4MB shared L3 cache 4GB (two 2GB SO-DIMMs) of 1333MHz DDR3 SDRAM AMD Radeon HD 6770M graphics processor with 1GB of GDDR5 memory on 2.4GHz configuration MacBook Air (13", 2011 model): 1.7GHz dual-core Intel Core i5 with 3MB shared L3 cache 4GB of 1333MHz DDR3 onboard memory Intel HD Graphics 3000 processor with 384MB of DDR3 SDRAM shared with main memory There's definitely a gap between them in terms of CPU speed and graphics, but what practical difference would this make on a day-to-day basis? On the one hand, I love the sleek, thin appearance of the Air. On the other hand, I don't want a machine that's going to be dog-slow when doing tasks such as running Virtual Machines, dual-booting to Windows and running multiple instances of Visual Studio, and maybe some light gaming. Is there going to be a major difference that makes the MacBook Pro a more attractive purchase?

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  • How to debug a website while running IIS 7?

    - by chobo2
    Hi I am running iis7 on my windows machine for testing purposes. Now I need to have access to the debugger so when something happens I can walk through it. Yet when I put debug lines on my site nothing happens. So I am guessing I need more stuff setup to make debugging to work. Everything is on the same machine. I have iis 7 on the same machine setup and I have Visual studios setup on my machine.

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  • Website with large number of users keeps going down due to memory leaks:Tomcat6 and Java 6

    - by user1766478
    We host many websites on one of our two virtual servers. We use tomcat 6 and Java 6. It is an MVC model with a hibernate like layer. The problem is, one of our biggest clients with the most number of members, keeps crashing the server every 6-8 hours(precisely in the mornings when most members login) We have been having this issue for 4 days now. Trying to figure out the problem but we suspect memory leaks. Any suggestions?

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  • Alternatives for heapdumps creation with higher performance than jmap?

    - by Christian
    Hi, I have to create heapdumps, which works nice with jmap. My problem is, that jmap takes very long to create the heapdump file. Especially when the heap is getting bigger ( 1GB) it is taking too long. One situation as example: When the server gets into trouble with the heapspace, I want to restart it automatically and create a heapdump before the restart. This works, but takes too long to write the heapdump. This way the server is down for too long. The heapdump creation takes longer than one hour. I know about -XX:+HeapDumpOnOutOfMemoryError, but most of the time I can find the memory problem before the exception is thrown by the jvm. Is there an alternative to jmap which writes the heapdumps faster? A special solution for the example above would also be appreciated. This question is a mix between programming and system-administration, but I think I'm at the right place here.

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  • when i try to access website without www. i get access denied.

    - by madphp
    I have an apache web server on a debian machine. Im using virtualmin to administer virtual hosts. I have two sites on this server right now, when i try to access one site without the www in the URL i get an access denied. The other site is fine. The site with the problem is a cakephp app and has the following .htaccess file in the public_html folder. <IfModule mod_rewrite.c> RewriteEngine on RewriteRule ^$ app/webroot/ [L] RewriteRule (.*) app/webroot/$1 [L] </IfModule> Below is the directives for the problem domain. SuexecUserGroup "#1001" "#1001" ServerName mydomain.net ServerAlias www.mydomain.net ServerAlias webmail.mydomain.net ServerAlias admin.mydomain.net DocumentRoot /home/mydomain/public_html ErrorLog /var/log/virtualmin/mydomain.net_error_log CustomLog /var/log/virtualmin/mydomain.net_access_log combined ScriptAlias /cgi-bin/ /home/mydomain/cgi-bin/ ScriptAlias /awstats/ /home/mydomain/cgi-bin/ DirectoryIndex index.html index.htm index.php index.php4 index.php5 <Directory /home/mydomain/public_html> Options -Indexes +IncludesNOEXEC +FollowSymLinks +ExecCGI allow from all AllowOverride All AddHandler fcgid-script .php AddHandler fcgid-script .php5 FCGIWrapper /home/mydomain/fcgi-bin/php5.fcgi .php FCGIWrapper /home/mydomain/fcgi-bin/php5.fcgi .php5 </Directory> <Directory /home/mydomain/cgi-bin> allow from all </Directory> RewriteEngine on RewriteCond %{HTTP_HOST} =webmail.mydomain.net RewriteRule ^(.*) https://mydomain.net:20000/ [R] RewriteCond %{HTTP_HOST} =admin.mydomain.net RewriteRule ^(.*) https://mydomain.net:10000/ [R] RemoveHandler .php RemoveHandler .php5 IPCCommTimeout 31 <Files awstats.pl> AuthName "mydomain.net statistics" AuthType Basic AuthUserFile /home/mydomain/.awstats-htpasswd require valid-user </Files>

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  • Can I set a default domain for a Windows Authenticated website in IIS7?

    - by Michael Haren
    I have an intranet site using Windows Authentication. When users are prompted for credentials, they enter: User: domain\username Pass: SomePassword It'd be nice if they could leave off the domain\ part which would be filled in with a default domain. I'm willing to give up the ability to login with a server/machine account (non-domain) because we don't use that anyway. This seems to be possible with BasicAuth but I can't seem to find a reference for how to do it with WindowsAuth.

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  • How should I monitor memory usage/performance in SunOS/Solaris?

    - by exhuma
    Last week we decided to add some SunOS (uname -a = SunOS bbs-sam-belair 5.10 Generic_127128-11 i86pc i386 i86pc) machines into our running munin instance. First off, the machines are pre-configured appliances, so, I want to avoid touching the system too much without supervision of the service provider. But adding it to munin was fairly easy by writing a small socket-service (if anyone is interested, I put it up on github: https://github.com/munin-monitoring/contrib/tree/master/tools/pypmmn) Yesterday, I implemented/adapted the required plugins for our machines. And here the questions start: First, I have not found a way to determine detailed memory usage values. I get the total memory by running prtconf | grep Memory, and the free memory using vmstat. Fiddling together a munin-plugin, gives me the following graph: This is pretty much uninformative. Compare this to the default plugin for linux nodes which has a lot more detail: Most importantly, this shows me how much memory is actually used by applications. So, first question: Is it possible to get detailed memory information on SunOS with the default system tools (i.e. not using top)? Onto the next puzzle: Seeing the graphs, I noticed activity in the "Paging in/out" graphs, even though the memory graph still has unused memory: Upon further investigation, I found out that df reports that /tmp is mounted on swap. Drilling around on the web, I understood that df will display swap, but in fact, it's mounted as a tmpfs. Now I don't know if this explains the swap activity. The default munin-plugin for solaris uses kstat -p -c misc -m cpu_stat to get these values. I find it already strange that this is using the cpu_stat module. So maybe I simply misinterpret the "paging" graphs? Second question: Do the paging graphs indicate that parts of the memory are paged to disk? Or is the activity caused by file operations in /tmp?

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  • What kind of server hardware is roughly necessary to serve website to 10k users?

    - by jcmoney
    I've been looking at VPS's and the specs they offer for entry level setups seems somewhat surprising to me. I'm am new to this topic but many of VPS offer less than 512MB of memory and my laptop has 4GB of memory so I am curious what does it actually take in terms of hardware to serve say 10k users (say 5k daily active users)? I figure a large number of factors can probably sway this a lot but just for benchmarking, say the site is a social networking site written in php using mysql + apache that's not really doing anything unusual like serving lots of media. So essentially a very basic Facebook minus the absurd number of photos and videos. What about 100k users (50k daily active)? 1 million (500k daily active)? Thanks in advance.

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  • Can I use IIS to do ActiveDirectory single-sign-on for another website?

    - by brofield
    I'm trying to add Active Directory single-sign-on support to an existing SOAP server. The server can be configured to accept a trusted reverse-proxy and use the X-Remote-User HTTP header for the authenticated user. I want to configure IIS to be the trusted proxy for this service, so that it handles all of the Active Directory authentication for the SOAP server. Basically IIS would have to accept HTTP connections on port X and URL Y, do all the authentication, and then proxy the connection to a different server (most likely the same X and Y). Unfortunately, I have no knowledge of IIS or AD (so I am trying my best to learn enough to build this solution) so please be gentle. I would assume that this is not an uncommon scenario, so is there some easy way to do this? Is this sort of functionality built into IIS or do I need to build some sort of IIS proxy program myself? Is there a better option for getting the authentication done and the X-Remote-User HTTP header set than requiring IIS? Update: For example, what I am trying to create is: [CLIENT] [IIS] [AD] [SOAP-SERVER] 1. |---------------->| 2. |<--------------->|<---------->| 3. |--------------------------->| 4. |<---------------------------| 5. |<----------------| 1. POST to http://example.com/foo/bar.cgi 2. Client is not authenticated, so do authentication 3. Once validated, send request to server (X-Remote-User: {userid}) 4. Process request, send response 5. Forward response to client I need to know how to configure IIS to do the automatic authentication of the user using AD, and then to proxy the request to the actual server, sending the userid in the X-Remote-User HTTP header.

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  • Performance: Nginx SSL slowness or just SSL slowness in general?

    - by Mauvis Ledford
    I have an Amazon Web Services setup with an Apache instance behind Nginx with Nginx handling SSL and serving everything but the .php pages. In my ApacheBench tests I'm seeing this for my most expensive API call (which cache via Memcached): 100 concurrent calls to API call (http): 115ms (median) 260ms (max) 100 concurrent calls to API call (https): 6.1s (median) 11.9s (max) I've done a bit of research, disabled the most expensive SSL ciphers and enabled SSL caching (I know it doesn't help in this particular test.) Can you tell me why my SSL is taking so long? I've set up a massive EC2 server with 8CPUs and even applying consistent load to it only brings it up to 50% total CPU. I have 8 Nginx workers set and a bunch of Apache. Currently this whole setup is on one EC2 box but I plan to split it up and load balance it. There have been a few questions on this topic but none of those answers (disable expensive ciphers, cache ssl, seem to do anything.) Sample results below: $ ab -k -n 100 -c 100 https://URL This is ApacheBench, Version 2.3 <$Revision: 655654 $> Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/ Licensed to The Apache Software Foundation, http://www.apache.org/ Benchmarking URL.com (be patient).....done Server Software: nginx/1.0.15 Server Hostname: URL.com Server Port: 443 SSL/TLS Protocol: TLSv1/SSLv3,AES256-SHA,2048,256 Document Path: /PATH Document Length: 73142 bytes Concurrency Level: 100 Time taken for tests: 12.204 seconds Complete requests: 100 Failed requests: 0 Write errors: 0 Keep-Alive requests: 0 Total transferred: 7351097 bytes HTML transferred: 7314200 bytes Requests per second: 8.19 [#/sec] (mean) Time per request: 12203.589 [ms] (mean) Time per request: 122.036 [ms] (mean, across all concurrent requests) Transfer rate: 588.25 [Kbytes/sec] received Connection Times (ms) min mean[+/-sd] median max Connect: 65 168 64.1 162 268 Processing: 385 6096 3438.6 6199 11928 Waiting: 379 6091 3438.5 6194 11923 Total: 449 6264 3476.4 6323 12196 Percentage of the requests served within a certain time (ms) 50% 6323 66% 8244 75% 9321 80% 9919 90% 11119 95% 11720 98% 12076 99% 12196 100% 12196 (longest request)

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  • Can i create a website blacklist with Group Policy?

    - by jimmygee
    Like i can create "whitelist" functionality for blocking all sites and allowing some via the GP setting: "User Configuration Windows Settings Internet Explorer Maintenance Connection/Proxy Settings Exceptions - Do not use proxy server for addresses beginning with" Can i create also a blacklist option like this (or similar) in Group Policy?

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  • How to print a rendered website to pdf or vector graphics?

    - by Lo Sauer
    This is a crucial question to many: Searching the web, I have found several command line tools that allow you to convert a HTML-document to a PDF-document, however they all seem to use their own, and rather incomplete rendering engine, resulting in poor quality How can you print the rendered output of a modern web-browser to pdf, (and/or svg) whilst retaining as much vector graphics as possible? There is a solution called: webkit-pdf (which renders everything to bitmap graphics) I am looking for options, alternatives, suggestions perhaps even a printer-driver or webservices? Thanks

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  • PostgresQL on Amazon EBS volume, realistic performance, or move to something more lightweight?

    - by Peck
    Hi, I'm working on a little research project, currently running as an instance on ec2, and I'm hoping to figure out whether I'm going down the right path. We, like a thousand other people, are making use of some of twitters streaming feeds to do gather some data to have fun with and my db seems to be having problems keeping up, and queries take what seems to be a very long time. I'm not a DBA by trade, so I'll just dump some info here and add more if need be. System specs: ec2 xl, 15 gigs of ram ebs: 4 100 gb drives, raid 0. The stream we're getting we're looking at around 10k inserts per minute. 3 main tables, with the users we're tracking somewhere in the neighborhood of 26M rows currently. Is this amount of inserts on this hardware too much to ask out of ebs? Should take a look at some things with less overhead like mongodb?

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  • Why is lighttpd and fastcgi keeping sending me the *.scgi file instead of the website content?

    - by e-satis
    I have the following config: server.modules = ( "mod_compress", "mod_access", "mod_alias", "mod_rewrite", "mod_redirect", "mod_secdownload", "mod_h264_streaming", "mod_flv_streaming", "mod_accesslog", "mod_auth", "mod_status", "mod_expire", "mod_fastcgi" ) [...] fastcgi.server = ( ".php" => (( "bin-path" => "/usr/bin/php-cgi", "socket" => "/var/tmp/lighttpd/php-fastcgi.socket" + var.PID, "max-procs" => 1, "kill-signal" => 9, "idle-timeout" => 10, "bin-environment" => ( "PHP_FCGI_CHILDREN" => "200", "PHP_FCGI_MAX_REQUESTS" => "1000" ), "/pyapps/essai/blondes.fcgi" => ( "main" => ( "socket" => "/var/tmp/lighttpd/django-fastcgi.socket", ), ), "bin-copy-environment" => ( "PATH", "SHELL", "USER" ), "broken-scriptfilename" => "enable" ))) [...] $HTTP["host"] =~ "(^|www\.)cam\.com(\:[0-9]*)?$" { server.document-root = "/home/cam/web/" accesslog.filename = "/home/cam/log/access.log" server.errorlog = "/home/cam/log/error.log" server.follow-symlink = "enable" # files to check for if .../ is requested server.indexfiles = ( "index.php", "index.html", "index.htm", "index.rb") url.rewrite = ( "^(/blondes/.*)$" => "/pyapps/essai/blondes.fcgi$1" ) } I have the following dir tree: /home/tv/web/ `-- pyapps `-- essai `-- __init__.py `-- blondes.fcgi `-- blondes.pid `-- django-fcgi.py `-- manage.py `-- manage.pyo `-- plop `-- settings.py `-- urls.py No error when restarting lighthttpd. The I run: ./manage.py runfcgi method=prefork socket=/var/tmp/lighttpd/django-fastcgi.socket daemonize=false pidfile=blondes.pid No errors neither. I then go to http://cam.com/blondes/. I offers me to download an empty file. I checked permissions but everything is set to the same user and group, and they work for the PHP site. The file /var/tmp/lighttpd/django-fastcgi.socket exists. When I reload the page, I got no output in error logs, nor in the manage.py runfcgi command. I probably missed something obvious, but what ?

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  • How to best tune my SAN/Initiators for best performance?

    - by Disco
    Recent owner of a Dell PowerVault MD3600i i'm experiencing some weird results. I have a dedicated 24x 10GbE Switch (PowerConnect 8024), setup to jumbo frames 9K. The MD3600 has 2 RAID controllers, each has 2x 10GbE ethernet nics. There's nothing else on the switch; one VLAN for SAN traffic. Here's my multipath.conf defaults { udev_dir /dev polling_interval 5 selector "round-robin 0" path_grouping_policy multibus getuid_callout "/sbin/scsi_id -g -u -s /block/%n" prio_callout none path_checker readsector0 rr_min_io 100 max_fds 8192 rr_weight priorities failback immediate no_path_retry fail user_friendly_names yes # prio rdac } blacklist { device { vendor "*" product "Universal Xport" } # devnode "^sd[a-z]" } devices { device { vendor "DELL" product "MD36xxi" path_grouping_policy group_by_prio prio rdac # polling_interval 5 path_checker rdac path_selector "round-robin 0" hardware_handler "1 rdac" failback immediate features "2 pg_init_retries 50" no_path_retry 30 rr_min_io 100 prio_callout "/sbin/mpath_prio_rdac /dev/%n" } } And iscsid.conf : node.startup = automatic node.session.timeo.replacement_timeout = 15 node.conn[0].timeo.login_timeout = 15 node.conn[0].timeo.logout_timeout = 15 node.conn[0].timeo.noop_out_interval = 5 node.conn[0].timeo.noop_out_timeout = 10 node.session.iscsi.InitialR2T = No node.session.iscsi.ImmediateData = Yes node.session.iscsi.FirstBurstLength = 262144 node.session.iscsi.MaxBurstLength = 16776192 node.conn[0].iscsi.MaxRecvDataSegmentLength = 262144 After my tests; i can barely come to 200 Mb/s read/write. Should I expect more than that ? Providing it has dual 10 GbE my thoughts where to come around the 400 Mb/s. Any ideas ? Guidelines ? Troubleshooting tips ?

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  • Can enabling a RAID controller's writeback cache harm overall performance?

    - by Nathan O'Sullivan
    I have an 8 drive RAID 10 setup connected to an Adaptec 5805Z, running Centos 5.5 and deadline scheduler. A basic dd read test shows 400mb/sec, and a basic dd write test shows about the same. When I run the two simultaneously, I see the read speed drop to ~5mb/sec while the write speed stays at more or less the same 400mb/sec. The output of iostat -x as you would expect, shows that very few read transactions are being executed while the disk is bombarded with writes. If i turn the controller's writeback cache off, I dont see a 50:50 split but I do see a marked improvement, somewhere around 100mb/s reads and 300mb/s writes. I've also found if I lower the nr_requests setting on the drive's queue (somewhere around 8 seems optimal) I can end up with 150mb/sec reads and 150mb/sec writes; ie. a reduction in total throughput but certainly more suitable for my workload. Is this a real phenomenon? Or is my synthetic test too simplistic? The reason this could happen seems clear enough, when the scheduler switches from reads to writes, it can run heaps of write requests because they all just land in the controllers cache but must be carried out at some point. I would guess the actual disk writes are occuring when the scheduler starts trying to perform reads again, resulting in very few read requests being executed. This seems a reasonable explanation, but it also seems like a massive drawback to using writeback cache on an system with non-trivial write loads. I've been searching for discussions around this all afternoon and found nothing. What am I missing?

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  • iperf max udp multicast performance peaking at 10Mbit/s?

    - by Tom Frey
    I'm trying to test UDP multicast throughput via iperf but it seems like it's not sending more than 10Mbit/s from my dev machine: C:\> iperf -c 224.0.166.111 -u -T 1 -t 100 -i 1 -b 1000000000 ------------------------------------------------------------ Client connecting to 224.0.166.111, UDP port 5001 Sending 1470 byte datagrams Setting multicast TTL to 1 UDP buffer size: 8.00 KByte (default) ------------------------------------------------------------ [156] local 192.168.1.99 port 49693 connected with 224.0.166.111 port 5001 [ ID] Interval Transfer Bandwidth [156] 0.0- 1.0 sec 1.22 MBytes 10.2 Mbits/sec [156] 1.0- 2.0 sec 1.14 MBytes 9.57 Mbits/sec [156] 2.0- 3.0 sec 1.14 MBytes 9.55 Mbits/sec [156] 3.0- 4.0 sec 1.14 MBytes 9.56 Mbits/sec [156] 4.0- 5.0 sec 1.14 MBytes 9.56 Mbits/sec [156] 5.0- 6.0 sec 1.15 MBytes 9.62 Mbits/sec [156] 6.0- 7.0 sec 1.14 MBytes 9.53 Mbits/sec When I run it on another server, I'm getting ~80Mbit/s which is quite a bit better but still not anywhere near the 1Gbps limits that I should be getting? C:\> iperf -c 224.0.166.111 -u -T 1 -t 100 -i 1 -b 1000000000 ------------------------------------------------------------ Client connecting to 224.0.166.111, UDP port 5001 Sending 1470 byte datagrams Setting multicast TTL to 1 UDP buffer size: 8.00 KByte (default) ------------------------------------------------------------ [180] local 10.0.101.102 port 51559 connected with 224.0.166.111 port 5001 [ ID] Interval Transfer Bandwidth [180] 0.0- 1.0 sec 8.60 MBytes 72.1 Mbits/sec [180] 1.0- 2.0 sec 8.73 MBytes 73.2 Mbits/sec [180] 2.0- 3.0 sec 8.76 MBytes 73.5 Mbits/sec [180] 3.0- 4.0 sec 9.58 MBytes 80.3 Mbits/sec [180] 4.0- 5.0 sec 9.95 MBytes 83.4 Mbits/sec [180] 5.0- 6.0 sec 10.5 MBytes 87.9 Mbits/sec [180] 6.0- 7.0 sec 10.9 MBytes 91.1 Mbits/sec [180] 7.0- 8.0 sec 11.2 MBytes 94.0 Mbits/sec Anybody has any idea why this is not achieving close to link limits (1Gbps)? Thanks, Tom

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