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• Linux memory fragmentation

  - by Raghu

  Hi all, Is there a way to detect memory fragmentation on linux ? This is because on some long running servers I have noticed performance degradation and only after I restart process I see better performance. I noticed it more when using linux huge page support -- are huge pages in linux more prone to fragmentation ? I have looked at /proc/buddyinfo in particular. I want to know whether there are any better ways(not just CLI commands per se, any program or theoretical background would do) to look at it.

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• Should I use 802.11n with a 15 Mbps ISP (Comcast Cable)?

  - by stackoverflowuser2010

  I currently own a LinkSys-WRT54GL 802.11a/b/g wireless router, and my ISP is Comcast Cable providing me with 15 Mbps (that's bits per second, I believe) download speed. I am wondering if there is any benefit with using an 802.11n wireless router to access the Internet? The maximum theoretical speed of the WRT54GL router is 54 Mbps (802.11g), which is faster than the 15 Mbps provided by my ISP. I know that 802.11n has a max bandwidth of 300 Mbps, and it would help for intra-house transfers, such as streaming video from one computer to another. But is there any benefit to 802.11n for Internet activity, such as web browswing, gaming, and streaming video from Netflix?

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• How to automate an Amazon EC2 instance startup, execution of some commands and shutdown?

  - by Howiecamp

  I need to download 100 GB of files (it’s in about 150 files) within a 7 day period before they expire. The download is rate-limited by the host so it takes MUCH longer than the theoretical transfer rate based on normal Internet speeds. I have a script of curl http://curl.haxx.se/docs/manpage.html commands - one line per file. I had the idea of automatically spinning up n EC2 instances, executing the command and FTPing the files to a central location, then shutting down the machines. How would I do this? I don't care whether it's Linux or Windows.

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• Sun Grid Engine: Automatically Terminating Idle Interactive Jobs

  - by dmcer

  We're considering using Sun Grid Engine on a small compute cluster. Right now, the current set up is pretty crude and just involves having people ssh to an open machine to run their jobs. We'd like to allow interactive jobs, since that should ease the transition from manually starting jobs to starting them using qsub. But, there is some concern that, if we do, people might accidentally leave their interactive sessions idle and block other jobs from being run on the machines. The issue isn't just theoretical, since we previously tried using OpenPBS and there was a problem with people opening up an interactive job in a screen session and essentially camping on a machine. Is there anyway to configure SGE to automatically kill idle interactive jobs? It looks like this was requested as an enhancement (Issue #:2447) way back in 2007. But, it doesn't seem like the request ever got implemented.

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• How should I host a site that could potentially get a short spike in traffic of 1000%+

  - by James Simpson

  This is a purely theoretical question, but what if I had a site that would normally only get a couple thousand hits a day, but for a few days each month that could shoot to several hundred thousand or even several million hits over the period of 1-3 days. The site would be pretty bare-bones (as in, 2-3 total pages with 1-2 max MySQL queries on each page and some PHP), so bandwidth wouldn't be the issue, but sheer volume taking down the site would be the main concern. Cloud hosting seems like the best way to go, but would something like Amazon EC2, MediaTemple, or something else be the right choice in this case?

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• How to check the version of the dynamic linker?

  - by netvope

  If I run a binary compiled on a newer Linux distro on an older Linux distro, I may get an error like this: a.out: error while loading shared libraries: requires glibc 2.5 or later dynamic linker How can I check the version of the dynamic linker in a Linux system? Is it provided by a package? If so, what's the name of the package? And a theoretical question: Is it possible to update the dynamic linker? (I don't think I'm going to do this but I just want to know.)

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• AAC 256kbit to MP3 320kbit conversion. I know it's lossy, but how?

  - by Fabian Zeindl

  Has anyone ever transcoded music from a high-quality aac to an mp3 (or vice-versa). The internet is full of people who say this should never be done, but apart from the theoretical standpoint that you can only lose information, does it matter in practise? is the difference perceivable, except on studio-equipment? does the re-encoding actually lose much information? If, p.e., high frequences are chopped away by the initial compression, those frequencies aren't there anymore, so this part of the compression-algorithm won't touch the data during the second compression. Am i wrong?

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• Advise on VMWare hardware requirements and host OS

  - by edwin.nathaniel

  Hi All, I'm a newbie developer wanting to learn a bit about Virtualization (from the IT point of view, not theoretical/academic). What I'd like to do: Prepare a machine Install VMWare or VirtualBox Prepare 3 Guest OSes (one for Win2k8 server, 2 for Ubuntu Server) Win2k8 will run SQL Server 2k8 and IIS (for ASP.NET MVC deployment) 1 Ubuntu Server for Drupal, SugarCRM, MediaWiki, typical LAMP stuff 1 Ubuntu Server for Java (Tomcat/Jetty + MySQL/PostgreSQL) What I'd like to know: What would be the ideal Host OS such that the Host OS should not spend too many resources on itself but should boost these instances of VMs (e.g: does Win2k8 performs better vs Linux?) What would be the ideal machine for this (preferably AMD base chip) I'm not expecting the best performance out of this setup, just a decent one to host one drupal instance, one ASP.NET MVC (future, not now), and one Tomcat/Jetty instance. NB: If you have a better suggestions on the setup, feel free to let me know (e.g: maybe Drupal and Tomcat can be in one instance but move the database to another instance instead of 1 instance map to 1 webserver and 1 dbserver). Thank you.

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• Why does storage's performance change at various queue depths?

  - by Mxx

  I'm in the market for a storage upgrade for our servers. I'm looking at benchmarks of various PCIe SSD devices and in comparisons I see that IOPS change at various queue depths. How can that be and why is that happening? The way I understand things is: I have a device with maximum (theoretical) of 100k IOPS. If my workload consistently produces 100,001 IOPS, I'll have a queue depth of 1, am I correct? However, from what I see in benchmarks some devices run slower at lower queue depths, then speedup at depth of 4-64 and then slow down again at even larger depths. Isn't queue depths a property of OS(or perhaps storage controller), so why would that affect IOPS?

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• Very low throughput on 10GbE network

  - by aix

  I have two Linux machines, each equipped with a Solarflare SFN5122F 10GbE NIC. The two NICs are connected together with an SFP+ Direct Attach cable. I am using netperf to measure TCP throughput between the two machines. On one box, I run: netserver and on the other: netperf -t TCP_STREAM -H 192.168.x.x -- -m 32768 I get: MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.x.x (192.168.x.x) 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 32768 10.02 1321.34 The measured throughput is 1.3Gb/s. This is 7.5x below the theoretical maximum, and only 30% faster than 1GbE. What steps can I take to troubleshoot this?

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• Right Drag on Mac

  - by Mafuba

  How do you perform a right-click-drag operation on Mac hardware? I know you can right click, but there does not seem to be a right click drag gesture. In my specific case I am using a MacBook Pro, and I am in a Windows environment. The question is more than just theoretical. I ask because there is functionality that uses this gesture, at least in the Windows world. For example, right now I'm trying to do a copy and rename in the TortoiseSVN repository browser. I think there are things you can do with a right drag in graphical editors like Photoshop as well. In windows you get a context menu when you right drag files. For those familiar with the software, I know I can do it in other ways; I'm not looking for workarounds to specific problems.

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• CPU load, USB connection vs. NIC

  - by T.J. Crowder

  In general, and understanding the answer may vary by manufacturer and model (and driver, and...), in consumer-grade workstations with integrated NICs, does the NIC rely on the CPU for a lot of help (as is typically the case with a USB controller, for instance), or is it fairly intelligent and capable on its own (like, say, the typical Firewire controller)? Or is the question too general to answer? (If it matters, you can assume Linux.) Background: I'm looking at connecting a device (digital television capture) that will be delivering ~20-50 Mbit/sec of data to a somewhat under-powered workstation. I can get a USB 2 High-speed device, or a network-attached device, and am interested in avoiding impacting the CPU where possible. Obviously, if it's a 100Mbit NIC, that's roughly half its theoretical inbound bandwidth, whereas it's only roughly a tenth of the 480 Mbit/second the USB 2 "High Speed" interface. But if the latter requires a lot of CPU support and the former doesn't...

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• Is it possible to host a website in the 'ether' of the Internet -- not on a server -- so that it can

  - by Chris Altman

  This is a theoretical problem I am curious about. Websites are hosted on servers. Servers can be taken offline. Is it possible to host a website in the 'ether' of the Internet -- not on a server -- so that it cannot be taken down? One example, is that the website is hosted on other websites, like a parasite. Another is that it is assembled through storing pieces on DNS machines, routers, etc., so that it get assembled on the fly. The purpose is that this website could live forever because no one person can remove it. The answers I am looking for are plausible idea/approaches on technically how this could be built.

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• Is it possible to host a website in the 'ether' of the Internet -- not on a server -- so that it cannot be taken down? [closed]

  - by Christopher Altman

  This is a theoretical problem I am curious about. Websites are hosted on servers. Servers can be taken offline. Is it possible to host a website in the 'ether' of the Internet -- not on a server -- so that it cannot be taken down? One example, is that the website is hosted on other websites, like a parasite. Another is that it is assembled through storing pieces on DNS machines, routers, etc., so that it get assembled on the fly. The purpose is that this website could live forever because no one person can remove it. The answers I am looking for are plausible idea/approaches on technically how this could be built.

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• Remove server from loadbalancer [on hold]

  - by Cris

  Our datacenter is load balancing the traffic to our weblogic servers based on an application deployed on each server called probe.ear It is a simple java app which is accessed by the loadbalancer and if it accessible it will redirect traffic to this server as well. When we want to remove one node from the loadbalancer we just stop the probe app and new traffic is not redirected to it BUT I am asking myself what about the current requests? The responses for the current requests are executed (completed). I did not had time to test (will do that first thing when go back to work) but on theoretical level for me it make sense to do so unless the loadbalancer has some special settings. Does my reasoning make sense to you? Just to make it clear since it was reported the question is not clear. Is there a way to configure a load balancer in a way that from a specific moment will not redirect traffic to a certain server without reseting the current requests ?

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• perfmon reporting higher IOPs than possible?

  - by BlueToast

  We created a monitoring report for IOPs on performance counters using Disk reads/sec and Disk writes/sec on four servers (physical boxes, no virtualization) that have 4x 15k 146GB SAS drives in RAID10 per server, set to check and record data every 1 second, and logged for 24 hours before stopping reports. These are the results we got: Server1 Maximum disk reads/sec: 4249.437 Maximum disk writes/sec: 4178.946 Server2 Maximum disk reads/sec: 2550.140 Maximum disk writes/sec: 5177.821 Server3 Maximum disk reads/sec: 1903.300 Maximum disk writes/sec: 5299.036 Server4 Maximum disk reads/sec: 8453.572 Maximum disk writes/sec: 11584.653 The average disk reads and writes per second were generally low. I.e. for one particular server it was like average 33 writes/sec, but when monitoring in real-time it would often spike up to several hundreds and also sometimes into the thousands. Could someone explain to me why these numbers are significantly higher than theoretical calculations assuming each drive can do 180 IOPs? Additional details (RAID card): HP Smart Array P410i, Total cache size of 1GB, Write cache is disabled, Array accelerator cache ratio is 25% read and 75% write

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• Is it possible to dynamically adjust the priority of outgoing emails?

  - by davethegr8

  This is more of a theoretical question, but is it possible to dynamically, and on an ongoing basis, adjust the priority of emails in the mail queue? For example, for all mail, set it's priority (p) to 1 (meaning send immediately). If N emails in the last M share similar or identical content, adjust the priority of this email such that it's priority is in the range [0..1] so that p is equal to 1 - N/M and other email can get sent before the similar/identical stuff. Or, if you have another idea or standard what is it? Some background: Someone put a mail() call in an infinite loop... And now we have to wait for the mail queue to catch up before anyone can send or receive mail again.

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• Xen and Ubuntu?

  - by wag2639

  How does one properly approach having Ubuntu servers on a Xen hypervisor? I don't have any experience with RAID or Xen other than from a theoretical level. Additional requirements: Use with mdadm Software RAID 5 (can be on separate disks) that multiple instances with access Paravirtualized Ubuntu Server guests instances Possible ideas for now: Ubuntu host (dom0) with ubuntu-xen-server package (this purportedly isn't supported) dom0 host will "own" RAID 5 partition More Ubuntu servers as guests Citrix XenServer bare-metal host XenServer will own RAID Citrix XenServer bare-metal host Ubuntu guest instance creates and owns RAID Questions and concerns: Can Ubuntu be used as a dom0 Xen host? Can XenServer install packages such as mdadm and create a partition? Can multiple guest access (R + W) to the same data partition (RAID)? Note: since it may have a bearing on support, I'm referring to Ubuntu Server 10.04

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• How frequent are network partitions on cloud services?

  - by roja

  Much is made of the CAP trade-off for data storage where conflicts can be introduced if there is a network partition. My question is there any evidence that this is a problem that arises with any significant frequency in modern cloud IAAS services e.g.; EC2, Azure, Rackspace. Is it a problem which, despite being a theoretical roadblock in constructing idealised distributed systems is, in fact, a non-issue for all practical concerns? Has anyone experienced a network partition within one of these systems (within a single data-centre?) If so would you be willing to share any details?

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• Workaround for API limits [closed]

  - by blunders

  Problem: Planning on building out a client services company that requires access to APIs. Most APIs are limited based on user, IP, etc. - and even though the API calls would be on a per client basis, there's no way to get usage not tied to IPs. (Theoretical) Solution: Have each client install on their network a proxy/VPN that would allow my systems to connect and use their assigned usage. So, it's possible there's a better solution than the one I've thought of, but it's the only one I've been able to come up with.

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• Windows 7 - Move open programs more freely on the taskbar

  - by SalamiArmi

  When I used Windows XP last year, I had a program called Taskix which let me move the tabs in the taskbar around for programs in any order I wanted. Now that I have Windows 7, a similar function comes built into the operating system - however, it isn't as flexible as Taskix was in XP. Theoretical situation: 1. Open a folder named #1 2. In folder #1, open an instance of a program 3. Open a folder named #2 4. In folder #2, open an instance of the same program that was opened in step 2. After doing this, I will have (in order, on the taskbar) 2 folders open and 2 instances of the programs open. My question really is: Is there any way to fight this automatic ordering of tabs on the taskbar? A registry hack or something would be best, but if there's a third party program out there, that would be nice to know about. Thanks!

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• What will Time Machine do when

  - by Joel Budgor

  When Time Machine says "I will delete the oldest files first" does it mean this literally. Here is a theoretical example. Source Drive: 300 GB, consisting of 1 280 GB file and a 1 GB file. Backup Drive: 300 GB The initial backup will backup both files, using 281 GB. If I modify the 1 GB file 21 times, what will Time machine do when I run out of room on the backup drive; Delete the original 280 GB because it is the oldest file or delete the oldest version of the file I have modified 21 times. I hope it would delete the oldest version of the file I have modified 21 times, but I want to be sure. Thanks, Joel Budgor

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• Straight-forward to Virtualise with XEN or KVM on IBM Server System x3650 M4 791562G?

  - by ChrisZZ

  I want to built a virtualised Server Environment using XEN or KVM. The virtual machines should be purely debian systems - so XEN or KVM should be a sane choice. Now while buying servers, I am confronted with the fact, that the vendors obviously only support commercial solution. I think, on a good server, one should be able to install uncommercial software as well - but of course sometimes systems have hardware, that requires drivers, that are not found in the OS Community. So I am asked the question: Is it straight-forward to use Debian with IBM Server System x3650 M4 791562G with Debian - or even virtualising the IBM Server System x3650 M4 791562G using XEN or KVM. I am sure there will always be a way to achieve this goal - but this way might have a high milage - so I am not asking, whether this is theoretical possible, but whether this should be straight-forward and practically easy to do, no major headaches to be expected.

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• What are the methods of separating network spaces in a LAN?

  - by dash17291

  Please detail me the methods. My thoughts: put the servers in separate (sub)networks the servers are forced to go through the firewall but no NAT is required assign more IP addresses to the internal interface of the server choosing gateway addresses from the clients and servers IP address ranges split DNS Netfilter/{iptables, ipset} could be heavily involved, I'm talking about Linux servers. See for example: Destination NAT Onto the Same Network from internal clients Please do not explain what is NAT or DNS. This is a theoretical question, but my poor English knowledge prevent me to describe it in a fancy fashion.

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• How to disable password change for openldap user?

  - by Keve

  Considering possible solutions for some improvements I run into this theoretical question and I couldn't find a satisfying answer. Some of you may have first-hand experience with this in practice, so here the question goes: How can I disable password changing for an OpenLDAP user? The account must stay enabled, allowed to log on to workstations and work as usual, but should not be able to change its own password. Can this be done? If so, how difficult is it to implement it? All suggestions are appreciated! For reference: Servers and workstations are to run a mixture of FreeBSD and OpenBSD. Accounts to get password disabled are student or generic workstation accounts. Environment is a school.

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