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• Windows Firewall Software to Filter Transit Traffic

  - by soonts

  I need to test my networking code for Nintendo Wii under the conditions when some specific Internet server is not available. Wii is connected to my PC with crossover ethernet cable. PC has 2 NICs. PC is connected to hardware router with ethernet cable. The hardware router serves as NAT and has an internet connected to its uplink. I set the Wii to be in the same lan as PC by using Windows XP Network bridge. I can observe the WII network traffic using e.g. Wireshark sniffer. Is there a software firewall that can selectively filter out transit traffic? (e.g. block outgoing TCP connections to 123.45.67.89 to port 443) I tried Outpost Pro 2009 and Comodo. Outpost firewall blocks all transit traffic with it's implicit "block transit packet" rule. If the transit traffic is explicitly allowed by creating the system-wide low level rule, then it's allowed completely and no other filter can selectively block it. Comodo firewall only process rules when the packet has localhost's IP as either source or destination, allowing the rest of the traffic. Any ideas? Thanks in advance! P.S. Platform is Windows XP 32 bit, no other OSes is allowed, Windows ICS (Internet Connection Sharing) doesnt work since the Wii is unable to connect, becides I don't like the idea of adding one more level of NAT.

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• Asus K55VM usb 3.0 issue

  - by user2141481

  Good day superusers! I own the above laptop and I found out that there are some unknown and unusual issues with usb 3.0 ports. I haven't noticed anything strange until now. I got a new toshiba usb 3.0 external hdd and when I try to copy larger amount of data from my disk to the external hdd, the OS(windows 7) randomly starts ignoring the external hdd. It doesn't shut it down, it kinda just stops responding but the light on the hdd is still lit. I get an error that the files cannot be copied. I have reinstalled windows 7, installed all drivers(including intel chipset drivers of course) and the issue is still present. It acts normal when copying small amount of data. Also, I heard that some intel chipsets have an issue with usb, something about the connectors not transferring power when the usb device enters some kind of "low power mode" causing the device to stop responding and you need to plug it out and in again. But the thing is, my Intel® Chief River Chipset HM76 is not on the list of affected hardware(not ENTIRELY sure though). If anyone has any idea of what the problem to this might be, I'd be greatful. Edit: The hdd works perfectly fine even for large amounts of data if plugged in the usb 2.0 port!

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• Website has become slower on a VPS, was much fast on a shared host. What's wrong?

  - by Arpit Tambi

  My shared host suspended my website stating system overload, so I moved my website to a VPS which has 4GB RAM. But for some reason the website has become very slow. This is the vmstat output - procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------ r b swpd free buff cache si so bi bo in cs us sy id wa st 1 0 0 3050500 0 0 0 0 0 1 0 0 0 0 100 0 0 Here's the Apache Benchmark output for a STATIC html page I ran on the server itself - Benchmarking www.ask-oracle.com (be patient)...apr_poll: The timeout specified has expired (70007) Total of 20 requests completed Update: Server Config: List item Centos 5.6 4 cores cpu 4 GB RAM LAMP stack with APC Wordpress Only one website It takes almost double time to load now, same website was much fast on shared hosting. I know I need to tweak some settings but have no clue where to start from? I have already tried to optimize apache, mysql etc. Update 2: CPU usage is low, see uptime output: 11:09:02 up 7 days, 21:26, 1 user, load average: 0.09, 0.11, 0.09 Update 3: When I load any webpage, browser shows "Waiting" for a long time and then page loads quickly. So I suspect server can accept only limited connections and holds extra connections in a waiting state. How to check this? Update 4: Following is the output on executing netperf TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to localhost.localdomain (127.0.0.1) port 0 AF_INET Recv Send Send Socket Socket Message Elapsed Size Size Size Time Throughput bytes bytes bytes secs. 10^6bits/sec 87380 16384 16384 10.00 9615.40 [root@ip-118-139-177-244 j3ngn5ri6r01t3]# Here are the Apache MPM settings from httpd.conf, do they look okay? <IfModule worker.c> StartServers 5 MaxClients 100 MinSpareThreads 50 MaxSpareThreads 250 ThreadsPerChild 125 MaxRequestsPerChild 10000 ServerLimit 100 </IfModule>

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• Is there a way to run CUDA applications with the CUDA device being a secondary adapter?

  - by Slartibartfast

  I've been trying to run a CUDA program on a remote computer which has Windows 7 installed. The GPU is GeForce GTX 480. One of the problems I've been facing is that, the computer has two adapters, 1) Standard VGA Adapter 2) NVIDIA GeForce GTX 480 Even though this shows in the device manager. The desktop uses the standard VGA Adapter. I'm assuming this is because the Standard VGA is the primary adapter. Also the device manager shows that the monitor is connected to the standard VGA Adapter. In this scenario if i try to run any CUDA application it fails to recognise a CUDA capable device. Is it necessary for the NVIDIA adapter to be the primary one? Or is there any way to use CUDA when the graphics card is a secondary adapter. I've seen a few posts in the NVIDIA forums on this before, one suggests using another low cost NVIDIA card as the primary adapter, but that is currently not an option. I couldn't find any other solutions. Thanks I tried running the deviceQuery test from the NVIDIA GPU Computing Samples. This was the result i obtained CUDA Device Query (Runtime API) version (CUDART static linking) cudaGetDeviceCount FAILED CUDA Driver and Runtime version may be mismatched FAILED The driver version I'm using is 263.06. The CUDA version is 3.2 I ran the same test on my desktop which also has windows 7 and a GeForce GTX 465. The CUDA toolkit version is 3.2. The driver version was the same and the test passed, although it failed with an older driver.

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• repo sync "CyanogenMod/android_prebuilt" size and resume capability.?

  - by james

  I'm downloading CyanogenMod-10.1 source on a low speed broadband. About 4GB of source is downloaded . In that 4GB, there is a big project "CyanogenMod/android_frameworks_base" which alone took 1GB of download without any interruption. Ok now, after 4GB of download, my internet got disconnected and I had to stop (ctrl + z) repo sync while it was downloading the project "CyanogenMod/android_prebuilt". Before I stopped repo sync the android_prebuilt got downloaded till 250MB and is at 42percent. I checked the working folder and there is a file "tmp_pack_df5CKb" of size 250MB in the path "$WORKING_DIR/.repo/projects/prebuilt.git/objects/pack/" . Then I restarted repo sync and it was downloading the android_prebuilt project. But I'm not sure if it was downloading from start or resuming from 250MB. While downloading this time , the previous "tmp_pack_df5CKb" isn't deleted and the content is being downloaded to a new file "tmp_pack_HPfvFG". I heard repo sync cannot be resumed for a project. But here, since the previous file isn't deleted I want to ask if android_prebuilt is resuming or downloading from start again? Now that my high speed internet is over (current speed 256kbps), I'm not sure if I can download the remaining ~4GB if single project is in size 500 MB.

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• Setting up a Network Bridge on Linux VM (Windows 7 Host)

  - by GrandAdmiral

  I would like to use NetEm to simulate a low bandwidth environment while testing an Internet-connected device. My plan is to setup a bridge in a Linux VM (Linux Mint 13) on a Windows 7 host. Unfortunately I'm having trouble setting up the bridge. Then I can use NetEm in the Linux VM to limit the bandwidth to an external device. I went with the following script: ifconfig eth0 0.0.0.0 promisc up ifconfig eth1 0.0.0.0 promisc up Then create the bridge and bring it up: brctl addbr br0 brctl setfd br0 0 brctl addif br0 eth0 brctl addif br0 eth1 dhclient br0 ifconfig br0 up When I run that script, I see the following warning: Rather than invoking init scripts through /etc/init.d, use the service(8) utility, e.g. service smbd reload Since the script you are attempting to invoke has been converted to an Upstart job, you may also use the reload(8) utility, e.g. reload smbd The device connecting to the bridge is able to obtain an IP Address, but it can only ping the IP Address of the bridge (both are 10.2.32.xx). Then after a few minutes, other parts of our network go down. I'm not sure why, but once I kill the bridge the network is fine. Is it possible to setup a network bridge in a Linux VM? Do I need to do something else with the dhclient br0 part of the script? By the way, I'm using VirtualBox. The wired connection is eth0 and the wireless connection is eth1. The wired connection is connecting to the device and the wireless connection is going to the network. Both adapters are set up as bridged adapters with promiscuous mode set to "allow all".

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• Only half of RAM is recognized by BIOS

  - by Rick Crawford

  I got a Gigabyte GA-P35-DS3 mainboard. Some time ago I noticed that Windows only showed 2GB instead of 4GB. I don't know exactly what caused it anyway. I tried putting in each of the 4 x 1GB RAM modules one by one, and tried every slot one by one, until every stick and slot worked. However, then I tried adding one more at a time, and it kept showing 1GB, until I put in all 4, where it only showed 2 GB instead of 4 (in BIOS and windows 7 64bit). I tried replacing the BIOS battery since I've read that low battery could cause it. It didn't help though. I also bought 4GB new RAM (yes, it's supported, I checked it), and it's still the same, it only shows 2GB (or 3GB, when I put in 4 of the new and 2 of the old). I also did the latest BIOS update, and used default BIOS settings, but nothing of that helped. When my PC boots it shows "RAM modules used 2 and 3", when 4 sticks are in - or "0 and 1", when only 2 are in.

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• MSSQL Timing out, a couple of questions...

  - by user29000

  Hi, About once a week, my MSSQL server is timing out, or rather the machine runs out of RAM. This morning it reached 3.9GB of the available 4, with MSSQL taking up 2.5GB. I'm concerned that i've not configured SQL to release memory as it should, so I ran sp_who2 while the timeouts were occuring to see what process were running. If i could post the CSV datafile i would, however, there were 85 processes in total, mostly related to the Full Text service: FT Gatherer - About 35 of these running under the 'sa' account against the master database with status of either sleeping or background, many were dependant on other processes. Is that normal? MySite database - There were only 5 processes for the one active site/database and all were either sleeping or suspended - but their lastBatch dates were set to 1/12/2020. Is that normal? The datbase is only about 20mb in size the traffic levels are very low, so i'm thinking of maybe limiting the amount of RAM SQL has access to (from unlimted to maybe 2GB). Any thoughts / advise would be appreciated. Mny thanks Ben

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• Send keystrokes simultaneously to both host and slave over internet?

  - by donodarazao

  I would like to watch movies with a friend who lives far away from me. For this, the playback should be synchronized on both our pc. However, we have some constraints: Due to our low bandwidth internet, any form of streaming solution wouldn't work. We do however both have the same copy of the movie on our harddisks. We use movies to learn languages and because of this, we very frequently pause and rewind. The typical "3...2...1...go!" solution over skype wouldn't work because it would soon get out of sync. I imagine an approach that sends keystrokes simultaneously to both our pc would work (for example, if I press space to pause the movie at my pc, space should also be send to his pc). Any ideas how this could be realized? I looked into Synergy and InputDirector, but both neither seem to be an option, because I don't want to see the desktop of my friend, I want to see my desktop Keystrokes should be sent simultaneously to both pc, not just to one pc We have both Windows 7x64, and we might use any media player (VLC, XBMC,...).

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• What is the optimum way to secure a company wide wiki?

  - by Mark Robinson

  We have a wiki which is used by over half our company. Generally it has been very positively received. However, there is a concern over security - not letting confidential information fall into the wrong hands (i.e. competitors). The default answer is to create a complicated security matrix defining who can read what document (wiki page) based on who created it. Personally I think this mainly solves the wrong problem because it creates barriers within the company instead of a barrier to the external world. But some are concerned that people at a customer site might share information with a customer which then goes to the competitor. The administration of such a matrix is a nightmare because (1) the matrix is based on department and not projects (this is a matrix organisation), and (2) because in a wiki all pages are by definition dynamic so what is confidential today might not be confidential tomorrow (but the history is always readable!). Apart from the security matrix, we've considered restricting content on the wiki to non super secret stuff, but off course that needs to be monitored. Another solution (the current) is to monitor views and report anything suspicious (e.g. one person at a customer site having 2000 views in two days was reported). Again - this is not ideal because this does not directly imply a wrong motive. Does anyone have a better solution? How can a company wide wiki be made secure and yet keep its low threshold USP? BTW we use MediaWiki with Lockdown to exclude some administrative staff.

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• Why does redis report limit of 1024 files even after update to limits.conf?

  - by esilver

  I see this error at the top of my redis.log file: Current maximum open files is 1024. maxclients has been reduced to 4064 to compensate for low ulimit. I have followed these steps to the letter (and rebooted): Moreover, I see this when I run ulimit: ubuntu@ip-XX-XXX-XXX-XXX:~$ ulimit -n 65535 Is this error specious? If not, what other steps do I need to perform? I am running redis 2.8.13 (tip of the tree) on Ubuntu LTS 14.04.1 (again, tip of the tree). Here is the user info: ubuntu@ip-XX-XXX-XXX-XXX:~$ ps aux | grep redis root 1027 0.0 0.0 66328 2112 ? Ss 20:30 0:00 sudo -u ubuntu /usr/local/bin/redis-server /etc/redis/redis.conf ubuntu 1107 19.2 48.8 7629152 7531552 ? Sl 20:30 2:21 /usr/local/bin/redis-server *:6379 The server is therefore running as ubuntu. Here are my limits.conf file without comments: ubuntu@ip-XX-XXX-XXX-XXX:~$ cat /etc/security/limits.conf | sed '/^#/d;/^$/d' ubuntu soft nofile 65535 ubuntu hard nofile 65535 root soft nofile 65535 root hard nofile 65535 And here is the output of sysctl fs.file-max: ubuntu@ip-XX-XXX-XXX-XXX:~$ sysctl -a| grep fs.file-max sysctl: permission denied on key 'fs.protected_hardlinks' sysctl: permission denied on key 'fs.protected_symlinks' fs.file-max = 1528687 sysctl: permission denied on key 'kernel.cad_pid' sysctl: permission denied on key 'kernel.usermodehelper.bset' sysctl: permission denied on key 'kernel.usermodehelper.inheritable' sysctl: permission denied on key 'net.ipv4.tcp_fastopen_key' as sudo ubuntu@ip-10-102-154-226:~$ sudo sysctl -a| grep fs.file-max fs.file-max = 1528687 Also, I see this error at the top of the redis.log file, not sure if it's related. It makes sense that the ubuntu user isn't allowed to change max open files, but given the high ulimits I have tried to set he shouldn't need to: [1050] 23 Aug 21:00:43.572 # You requested maxclients of 10000 requiring at least 10032 max file descriptors. [1050] 23 Aug 21:00:43.572 # Redis can't set maximum open files to 10032 because of OS error: Operation not permitted.

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• network will not work properly after having run TCP optimizer, but safe mode settings work perfectly. how to restore?

  - by michele

  I was experiencing some issues with my connection while playing online and I tried to optimize it by running TCP optimizer on my PC (Windows 7 64bit professional). I thought maybe the situation could improve. but it didn't. actually, I now get an extremely slow page loading time, probably due to a very low RWIN value of 1024. I understand that Windows 7 has a system to automatically adjust the RWIN value when needed. The setting from netsh is "normal" so I guess something else must be wrong. I tried every automatic tool out there to restore Windows' default values, but I had no success. I currently have what should be labeled as "default values" for everything TCP Optimizer initially changed, but the problem persists. The thing is, I just found out that running Windows in safe mode SOLVES the problem completely. The problem is that as soon as I reboot, I get the same issue all over again. So my question is: is there a way to use SAFE MODE network settings in NORMAL mode?

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• Why do hosts prefer Linux to Windows Server?

  - by iconiK

  So far I see a HUGE majority of hosts provide only Linux shared hosting, providing Windows only to VPS (or even to only dedicated servers). Why is it so? While Windows is a lot more expensive than Linux (though it depends on a lot of factors, not just initial and support license cost), it also provides ASP.NET, IIS and of course, Microsoft SQL Server. I know in the past it might have been because of cPanel being Linux only but now they have a Windows version. But still, why is Linux predominantly used on shared hosting? PHP works on both systems. IIS can be (and probably is) faster. MySQL runs on both systems as well. cPanel has a Windows version. Python, Perl, Ruby, all run on Windows as well. You even have MS SQL Server Express, which I find more superior than MySQL in both speed and features. Access is there for low usage requirements, as is SQLite (which is so great for quick small stuff). And with PowerShell you have a good alternative to the Unix shell. EDIT: I am looking for common reasons, I realize each hosting company (and/or it's clients) may have different needs. This becomes very important when you get to VPS or Cloud which give you a full operating system to use.

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• Setting up MySQL Linux slave with a Windows master

  - by philwilks

  I'm running a MySQL 5.0 database server on Windows Server 2008. The total size of the database is about 1Gb. I make daily backups, but I'd like to step up to having a slave server for extra protection. My thinking was that I wouldn't need the expense of a Windows machine to do this, and a Linux "cloud server" from RackSpace would do the job well for quite a low cost. However I have little experience with Linux, so I have a few questions... Does this sound like a good idea? Is there anything wrong with linking Windows and Linux MySQL servers? Does Linux have the equivalent of Remote Desktop Connection? If so can I use this from a Windows machine? Would a particular Linux distro be well suited to this task? RackSpace offer ArchLinux, CentOS, Debian, Fedora and Ubuntu. My immediate thinking is to go with Ubuntu as I've heard it's more friendly for people coming from a Windows background. Any comments you have would be very appreciated! Phil

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• Intermittent extrememly long response times when downloading documents

  - by pap

  I have a Java web application running om Tomcat 7 with an Apache httpd 2.2 fronting with mod_jk/AJP. One part of the application is serving files (up to 4mb size). Now, normally this all runs very smooth with stable, low response-times. However, in rare instances (<0.1% of downloads), the downloadtime will go beyond 1 minute. After activating the ThreadStuckValve in Tomcat, I can see that the long responses seem to be stuck at org.apache.tomcat.jni.Socket.sendbb(Native method) i.e network I/O. At most, these long-running downloads take 5 minutes, which I strongly suspect is because of the default 300 second timout in Apache 2.2 (http://httpd.apache.org/docs/2.2/mod/core.html, "TimeOut directive"). To me, this looks like network problems. The Apache timeout (if that is what is kicking in at the 5 minute mark) indicates that ACK packets are not being transmitted correctly. My questions are what could be causing this? Closed browser at receiving end but socket not signaled as closed properly? Packet loss or some other network failure in transit? Where would I start troubleshooting this? We're running Tomcat and Apache on Windows server 2008-R2 in a vmware virtualized server.

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• Data Store/Volume disconnecting. How to resume copy of VMDK?

  - by Serge

  I'm having an issue with my ESXi 4.1 hosts losing the datastore with FC SAN after a power outage. All 3 hosts disconnect so it's definitely a SAN issue. I've tried to resolve the issue on the SAN side with the SAN software support and Adaptec hardware support. No luck there. So I'm stuck with a SAN that will randomly disconnect the volume. I need to get the virtual machines (VMDK files) from the datastore. The problem is I can only get 5-20% before the data store disconnects. I have backups that are slightly older that I can use to replicate the VMDK differences to. What has not worked so far: Powering up the VMs, will boot up for 5-15 minutes then freeze vCenter migrate or clone of VM, will fail after similar period of time vCenter copy/paste of VMDK. Was able to get one 30GB VMDK and no luck after that. vMware Data Recovery. Fails at low %, can't resume, so next backup starts from begining. Veeam Backup & Recovery. Same as above, no resume function. If I can just find a backup solution that will resume from the failed spot that would solve my issue. Anyone have any ideas that I could try? EDIT 1 The SAN is Open-E DSS 6 running on a Supermicro 24 drive enclosure with 4 port Qlogic FC. Adaptec 52445 RAID card.

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• What is causing sudden freezing during running real-time program?

  - by Trevor Boyd Smith

  So I run a high intensive (CPU/GPU) real-time program. During normal execution suddenly everything freezes for 1-4 seconds. I opened "Process Explorer" in the background to help gain insight and maybe identify something. Here is what the CPU/GPU graphs looks like when I align them in time: Notice the 4 distinct drops in both the CPU/GPU. You can see that it goes from some sort of positive CPU/GPU usage to almost zero. These drops in the graph align with when the real-time program suddenly freezes. How do I find what is causing these sudden drops? NOTE: When you put your mouse over the graph it tells you the time, accurate to the second, for where your cursor is. Maybe this mouse over feature could be helpful in some way (e.g. what if you had a log of all processes every 100ms). EDIT: The real-time program is a video game and so I can't watch some sort of instrumentation while the video game is running. I need a solution that let's you look back in time somehow to see what was happening when the slow down occurred. EDIT: RE - Recording Data vs using real-time monitor: So the windows performance recorder is for some reason not recording what I expect it to record. So I switched to using "perfmon" and then opening it's "resource monitor". RE - Setting it up so I can view real-time monitor: In the video game I set it to spectate and then put the video game in "windowed" mode so that I can view the real time display that Resource Monitor has. Now that I can get semi-real time (only once per second... how do you get more than once per second?) I started looking at the various real time data readouts. Getting to the cause: I noticed a strong correlation in high disk IO and low CPU usage (which is also seen by having in-game freezing). How do you use resource monitor to find out who is doing all this offending disk IO?

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• Windows Action Center notification icon says Backup in Progress when no backup is occurring

  - by allquixotic

  How can I get Windows Action Center's little flag in the notification area to stop saying "Backup In Progress" on Windows 8? It's driving me nuts. I disabled the Windows Backup service completely and turned off File Recovery. Nothing that I can tell is using any disk I/O whatsoever, by examining Task Manager's resource monitor. It's just a visual cue that seems totally wrong considering my disk is only using about 50 KB/s of sporadic writes for superfetch etc. This wouldn't be a problem for me, since I rely on the knowledge that the Backup service is disabled and there's no disk activity, but I am trying to support a more traditional user who relies on visual cues from the operating system and trusts them over low-level observations like "...but the Windows Backup service is disabled!" Therefore this user still thinks that the backup is going on, even after the service is disabled. Technically, I think this is a bug in Windows 8. It really should not be displaying "Backup in Progress" if ... you know ... a backup, is not, in progress. Which it isn't. Is there a workaround?

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• Software/hardware to build video streaming server?

  - by Sasha Yanovets

  I am looking for a video streaming server solution, something like online TV server, with ability to make live broadcasts in the internet. What software could you recommend for that? What kind of hardware it should run on, should be there anything special? I am looking for a solution that could be scaled up to at least 1000 simultaneous users online with good resolution of video. I think it is good to have general answer on what direction to choose. But here more details on my specific case: I just looking for a solution almost from scratch. We have some video content that we've produced, but it is not delivered over internet yet. We do not tied to any particular vendor for now. We want to make 24 hours of steaming three 8 hour blocks with change of content every day. We want the ability to make regular live broadcasts. I guess we will need to have several options of streaming quality (low ~56 kb/s mid ~273 kb/s). Some terms just foreign to me (like play-truncation rate), if you could point out what parameters we should avare of, it would be great. Uplink to the internet is to be determined. We plan to start from something and scale up on the way. If you are already have some kind of media streaming server, just describe its configuration here (hardware, OS, software), peak number of concurrent users it serves. I think it could help people approaching this task.

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• Can any iSCSI NAS appliance replicate / clone a LUN to an external drive?

  - by Boden

  I would like to backup using Windows Imaging to some kind of NAS appliance. I believe this will require the NAS to support iSCSI. I would then like the appliance to support the replication of the iSCSI LUN to an external eSATA or USB disk connected directly to the appliance. I've found plenty of NAS appliances that can do iSCSI and replicate to an external drive, but none that I've found thus far can do both at once. That is, the devices can do iSCSI, but then the replication feature doesn't work. The idea here is to backup to an appliance located in a secure office far away from the server room. Offsite backups to external hard drive could be managed from the appliance. The benefits of such a setup would be: 1) very unlikely that fire or random theft would affect both server-room backup and "remote" backup appliance 2) offsite backups could be managed by multiple trusted people without granting access to server room 3) Windows imaging provides poor man's deduplication, so each backup volume can contain a decent backup history. I understand why this would be a non-trivial thing to implement, but I'm wondering if such a thing exists? Preferably a tabletop, low to medium cost device. Alternative solutions welcome. NOTE: I'm backing up very few but very large files, so file replication is not a good option.

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• Best practices for thin-provisioning Linux servers (on VMware)

  - by nbr

  I have a setup of about 20 Linux machines, each with about 30-150 gigabytes of customer data. Probably the size of data will grow significantly faster on some machines than others. These are virtual machines on a VMware vSphere cluster. The disk images are stored on a SAN system. I'm trying to find a solution that would use disk space sparingly, while still allowing for easy growing of individual machines. In theory, I would just create big disks for each machine and use thin provisioning. Each disk would grow as needed. However, it seems that a 500 GB ext3 filesystem with only 50 GB of data and quite a low number of writes still easily grows the disk image to eg. 250 GB over time. Or maybe I'm doing something wrong here? (I was surprised how little I found on the subject with Google. BTW, there's even no thin-provisioning tag on serverfault.com.) Currently I'm planning to create big, thin-provisioned disks - but with a small LVM volume on them. For example: a 100 GB volume on a 500 GB disk. That way I could more easily grow the LVM volume and the filesystem size as needed, even online. Now for the actual question: Are there better ways to do this? (that is, to grow data size as needed without downtime.) Possible solutions include: Using a thin-provisioning friendly filesystem that tries to occupy the same spots over and over again, thus not growing the image size. Finding an easy method of reclaiming free space on the partition (re-thinning?) Something else? A bonus question: If I go with my current plan, would you recommend creating partitions on the disks (pvcreate /dev/sdX1 vs pvcreate /dev/sdX)? I think it's against conventions to use raw disks without partitions, but it would make it a bit easier to grow the disks, if that is ever needed. This is all just a matter of taste, right?

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• What are the frequencies of current in computers' external peripheral cables and internal buses?

  - by Tim

  From Wikipedia, three different cases of current frequency are discussed along with the types of cables that are suitable for them: An Extra Ordinary electrical cables suffice to carry low frequency AC, such as mains power, which reverses direction 100 to 120 times per second (cycling 50 to 60 times per second). However, they cannot be used to carry currents in the radio frequency range or higher, which reverse direction millions to billions of times per second, because the energy tends to radiate off the cable as radio waves, causing power losses. Radio frequency currents also tend to reflect from discontinuities in the cable such as connectors, and travel back down the cable toward the source. These reflections act as bottlenecks, preventing the power from reaching the destination. Transmission lines use specialized construction such as precise conductor dimensions and spacing, and impedance matching, to carry electromagnetic signals with minimal reflections and power losses. Types of transmission line include ladder line, coaxial cable, dielectric slabs, stripline, optical fiber, and waveguides. The higher the frequency, the shorter are the waves in a transmission medium. Transmission lines must be used when the frequency is high enough that the wavelength of the waves begins to approach the length of the cable used. To conduct energy at frequencies above the radio range, such as millimeter waves, infrared, and light, the waves become much smaller than the dimensions of the structures used to guide them, so transmission line techniques become inadequate and the methods of optics are used. I wonder what the frequencies are for the currents in computers' external peripheral cables, such as Ethernet cable, USB cable, and in computers' internal buses? Are the cables also made specially for the frequencies? Thanks!

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• nginx: dump HTTP requests for debugging

  - by Alexander Gladysh

  Ubuntu 10.04.2 nginx 0.7.65 I see some weird HTTP requests coming to my nginx server. To better understand what is going on, I want to dump whole HTTP request data for such queries. (I.e. dump all request headers and body somewhere I can read them.) Can I do this with nginx? Alternatively, is there some HTTP server that allows me to do this out of the box, to which I can proxy these requests by the means of nginx? Update: Note that this box has a bunch of normal traffic, and I would like to avoid capturing all of it on low level (say, with tcpdump) and filtering it out later. I think it would be much easier to filter good traffic first in a rewrite rule (fortunately I can write one quite easily in this case), and then deal with bogus traffic only. And I do not want to channel bogus traffic to another box just to be able to capture it there with tcpdump. Update 2: To give a bit more details, bogus request have parameter named (say) foo in their GET query (the value of the parameter can differ). Good requests are guaranteed not to have this parameter ever. If I can filter by this in tcpdump or ngrep somehow — no problem, I'll use these.

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• Why do manufacturers not show all hardware power usage?

  - by Drew

  I find it slightly more difficult to build a computer when I do not know how much power is needed for a component. When selecting a power supply for a computer, it is difficult to know how large of one to get. You don't want to go too large for cost reasons and circuit reasons, but you don't want to go too low and not be able to properly use every component. For instance, a graphics card might say "Minimum of a 500 Watt power supply. (Minimum recommended power supply with +12 Volt current rating of 30 Amps.)" But it really needs 360W (12V * 30A). So why don't they just say "Uses 360W max and xxxW peak"? Processors, I have noticed are good at reporting their power usage, but aside from processors and sometimes graphics cards, power usage is easily found. What is the power consumed by the Blu-ray / DVD drives? By the HDDs/SSDs? By the Mobo? etc. Why are these questions not easily answered when building a machine?

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• Remote paging with Nagios when network is down and email won't work -- cellular modems and alternatives

  - by Quinten

  What is the best option for remote paging when network services are down? I'm looking for a solution that can let me know when network services are down during off-hours only, and especially when email/smtp services are out. Therefore, it needs to be redundant to our network and power supply. I'm imagining a cellular modem is one option. What's the price range for these? Is anybody using them and feel that they are worth the cost? I'm imagining that it's something we would end up sending an emergency page ~ 1x/month at most, so I'd like the pricing to reflect that--I don't mind a high per-page cost as long as it has a low recurring cost. Another option would be to expose at least one server to remote ping, and run a check script on a remote server. Are there paid options for this? Currently, we run Nagios on a Linux VM on a Windows 2008 Hyper-V host. It would be great if the solution would work in that environment, but I know it's tricky with external devices, and we could move Nagios to a standalone workstation if needed.

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