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  • Campus VLAN Segmentation - By OS?

    - by Moduspwnens
    We've been thinking through re-arranging our network and VLAN configuration. Here's the situation. We already have our servers, VoIP phones, and printers on their own VLANs, but our problem lies with end user devices. There are just too many to lump on the same VLAN without being hammered with broadcasts! Our current segmentation strategy has them split into VLANs like this: Student iPads Staff iPads Student Macbooks Staff Macbooks Gaming devices Staff (Other) Student (Other) *Note that our network has many more iPads and MacBooks than most. Since the primary reason we're splitting them is just to put them in smaller groups, this has been working for us (for the most part). However, this required our staff to maintain access control lists (MAC addresses) of all devices belonging in these groups. It also has the unfortunate side effect of illogically grouping broadcast traffic. For example, using this setup, students on opposite ends of campus using iPads will share broadcasts, but two devices belonging to the same user (in the same room) will likely be on completely separate VLANs. I feel like there must be a better way of doing this. I've done a lot of research and I'm having trouble finding instances of this kind of segmentation being recommended. The feedback on the most relevant SO question seems to point toward VLAN segmentation by building/physical location. I feel like that makes sense because logically, at least among miscellaneous end users, broadcasts will typically be intended for nearby devices. Are there other campuses/large-scale networks out there segmenting VLANs based on end-system OS? Is this a typical configuration? Would VLAN segmentation based on physical location (or some other criteria) be more effective? EDIT: I've been told that we will soon be able to dynamically determine device OS without maintaining access lists, although I'm not sure how much that affects the answers to the questions.

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  • Looking for recommendations on OCR problem - tabular numeric data

    - by ldigas
    I have 20 pages of experiment measurement data which I need to digitalize. The results are in tabular form, scanned in 600 dpi resolution, and as far as scans go, they came up pretty clean and readable. For an example of how it looks see here (but beware: it is a rather big scan; about 5Mb; no problem for any broadband connection, but dialups should approach with caution!) ... and I need it finished by sunday afternoon (:-o) <-- smiley in a state of panic (then why did't you start sooner?)... yea, yeah ... I know ... but, it came up late, and I wasn't thinking I was gonna need this data also. So, I'm looking for recommendations. I haven't much experience with OCR programs, save scanning a page or two of pure text, but just to mention, I haven't the wish also to test out every OCR program out there. So this isn't a "name your OCR favourite". What I'm looking is advice from someone who's done something like that, and his/hers experience on what would be the best way to undertake. I need the data in txt form but since it will have to be checked (by drawing it, and just simply watching whether some points "jump out") I'll probably be entering it in Excel at first.

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  • How to move Mdadm RAID drive (EBS based) to different AWS Instance

    - by Stanley
    We have a media-rich web application that is hosted on AWS. We have several Web Servers and we have an NFS server. On the NFS server (Linux server) we have several EBS volumes that are mounted and we've used mdadm to implement the different mounted volumes as a single RAID volume. The Web Servers simply access the NFS storage through a mount point. Amazon has now let us know that they will be performing power maintenance on this server in a couple of days time. Since all our media is on here it would render our site unusable for the hours while Amazon is working on it. We want to try and prevent this downtime. I was thinking that we can prevent server downtime by perhaps setting up a new server temporarily and attaching the EBS drives (raid volume) to that server and have our web servers point there during maintenance. This is a very high risk operation since this involves several terabytes of our production data. What would be the safe way to move over our logical raid drive (md0) to a new amazon instance? I was hoping that I could start with building the new server, mounting the ebs volumes and assembling the RAID partition using mdadm --assemble --scan before unmounting from the existing instance so that I can first test that everything works and thus having it mounted on two instances at the same time, but I don't believe that is possible with the way that filesystems work. How do I move a Linux software RAID to a new machine? suggests a way to move drives, but isn't really a cloud-based question. Perhaps there are simpler ways to prevent system downtime with our solution being hosted on the cloud? I have considered taking an EBS snapshot, but that tries to replicate all the many terabytes of mounted storage, so this is not a practical solution. Any ideas?

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  • sharing a folder between linux and windows over the internet

    - by valya
    Hello Currently my job is to make websites with Django. I use many things like virtualenv, PIL, etc. The problem is, I can't stand Linux on my desktop. I like it on servers, It's greate to use it over the SSH. But for desktop? No way. But for the development Linux is quite essential. Of course almost everything is ported to Windows, but it's not as simple to use as in Linux. For example, Windows shell is awful in comparison with Linux. So I've tried Cygwin, but it's too damn slow. Every time django dev server reloads, it tooks almost 20-30 seconds. In comparison, then using "native" python on Windows or Linux, it reloads instantly. Even worse, Cygwin makes all my system very slow. I've been thinking about it and have thought up a way to go. I can share a folder with my application with some Linux box. The devserver and everything will run on that box, while I'll be happy editing files and running the browser on my Windows 7. SSH shell is much quickier and handy than Cygwin. Currently there are no Linux boxes in my home network (except for my android phone :) but I have several VDS boxes with Debian. So, how do I share a Windows folder with VDS box? I can't rely on my desktop IP but I can rely on the VDS's one. I need sharing to be as quick as possible (well, 2-3 seconds ping is OK) and "native" for both systems, so I could use a folder like a normal folder in both Windows and Linux.

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  • Mac OS X Disk Encryption - Automation

    - by jfm429
    I want to setup a Mac Mini server with an external drive that is encrypted. In Finder, I can use the full-disk encryption option. However, for multiple users, this could become tricky. What I want to do is encrypt the external volume, then set things up so that when the machine boots, the disk is unlocked so that all users can access it. Of course permissions need to be maintained, but that goes without saying. What I'm thinking of doing is setting up a root-level launchd script that runs once on boot and unlocks the disk. The encryption keys would probably be stored in root's keychain. So here's my list of concerns: If I store the encryption keys in the system keychain, then the file in /private/var/db/SystemKey could be used to unlock the keychain if an attacker ever gained physical access to the server. this is bad. If I store the encryption keys in my user keychain, I have to manually run the command with my password. This is undesirable. If I run a launchd script with my user credentials, it will run under my user account but won't have access to the keychain, defeating the purpose. If root has a keychain (does it?) then how would it be decrypted? Would it remain locked until the password was entered (like the user keychain) or would it have the same problem as the system keychain, with keys stored on the drive and accessible with physical access? Assuming all of the above works, I've found diskutil coreStorage unlockVolume which seems to be the appropriate command, but the details of where to store the encryption key is the biggest problem. If the system keychain is not secure enough, and user keychains require a password, what's the best option?

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  • Millions of files in php's tmp error - how to delete?

    - by Jonatan Littke
    Hey. I've got a tmp-folder with 14 million php session files in my home directory. At least that's what I think it is, it's not like I could ls it or anything. How can I empty this folder? I've tried using find with the -exec rm {} \; commands but that didn't work. ls 'sess_0*' | xargs rm did neither. I'm currently running rm -rf tmp but after two hours the folder appears to be the same size. REFERENCE INFO: I suddenly encountered an error where SESSIONS could no longer be written to disk: [Mon Apr 19 19:58:32 2010] [warn] mod_fcgid: stderr: PHP Warning: Unknown: open(/var/www/clients/client1/web1/tmp/sess_8e12742b62aa68a3f9476ec80222bbfb, O_RDWR) failed: No space left on device (28) in Unknown on line 0 [Mon Apr 19 19:58:32 2010] [warn] mod_fcgid: stderr: PHP Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (/var/www/clients/client1/web1/tmp) in Unknown on line 0 I ran: $ df -h Filesystem Size Used Avail Use% Mounted on /dev/md0 457G 126G 308G 29% / tmpfs 1.8G 0 1.8G 0% /lib/init/rw udev 10M 664K 9.4M 7% /dev tmpfs 1.8G 0 1.8G 0% /dev/shm But as you can see, the disk isn't full. So I had a look in the syslog which says the following 20 times per second: kernel: [19570794.361241] EXT3-fs warning (device md0): ext3_dx_add_entry: Directory index full! This led me thinking to a full folder, obviously, but since my web folder only has 60k files (having counted them), I guessed it was the tmp folder (the local one, for this instance of php) that messed things up. Some commands I ran: $ sudo ls sess_a* | xargs rm -f bash: /usr/bin/sudo: Argument list too long find . -exec rm {} \; rm: cannot remove directory '.' find: cannot fork: Cannot allocate memory I'm running Debian Lenny, php5, ISPConfig, SuEXEC and Fast-CGI.

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  • What privilege level is required on a Windows client workstation on an ActiveDomain to break file lo

    - by Mike Burton
    I'm not sure if I should be asking this here or on StackOverflow, but here goes: I'm part of a team maintaining a document management application, and I'm trying to figure out Windows file locking permissions. We use a utility somebody downloaded years ago called psunlock to remotely close all locks on a file. We recently discovered that this does not work across different domains on our VPN. A little bit of digging lead me to the samba manual's discussion of file locking. I still don't really "get it", though. Does anyone have any insight to share into how the process of locking and breaking locks on files works in a network context? My thinking is that privileges are required both on the file appliance and on the client workstations which hold locks. Is that accurate? Can anyone give a more specific version? Ideally I'm looking for something along the lines of A user must have privilege level X in order to break locks held from a client workstation. In practice I'd be happy with a hotlink to a good white paper on the subject.

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  • Can't connect to research.microsoft.com on home Qwest DSL connection

    - by rakingleaves
    I have a puzzling issue regarding accessing research.microsoft.com from my home Qwest DSL connection. By default, I frequently get timeouts when accessing research.microsoft.com from Firefox, Safari, or Chrome on my Mac. I also cannot access the site from Internet Explorer in a Windows VM. However, I am able to access the site through proxify.com, so I know the site is not down. Furthermore, I haven't noticed problems accessing other sites (in particular, www.microsoft.com works fine). Also, I can access research.microsoft.com when I'm connected to networks other than my home Qwest DSL connection. Together, the above make me suspect a problem with either my router (Airport Express) or, more likely, my ISP. Anyone have any thoughts on how I can narrow down the problem further? I could call my ISP and tell them the above, but my feeling is that probably won't get me very far. I can get by browsing research.microsoft.com through a proxy, but it would be nice to figure out what's going on here and fix the problem. Oh, the only relevant discussion I found via Google was here: http://forums.whirlpool.net.au/forum-replies-archive.cfm/1311734.html Update: Thanks to those who have tried to help! I found one other thing while Googling that may be vaguely relevant: http://thedaneshproject.com/posts/supportmicrosoftcom-not-working-behind-squid/ Disabling the Accept-Encoding headers in Firefox actually didn't make a difference for me. I just thought the above might spark some other ideas about how mishandling of HTTP headers somewhere might be causing this problem. Thanks again! Another update: In case anyone is still thinking about this; I've found that I can't surf research.microsoft.com using the links text-based browser, but I can reliably download individual files with wget. Maybe that helps?

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  • Building a PC for Work and play? [closed]

    - by Derek Organ
    Ok, Its been a long time since I build my own PC so I'm looking to get back into it again and build a new one. First off budget is about €800 excluding the monitor and windows 7 licence and mouse. (just bought a new g500) I plan on using my computer for work, lots of applications open at once but none particularly excessive (photoshop being the most demanding, mostly coding tools) I also use it for some gaming, e.g. COD, Starcraft etc. One thing I do want to do eventually is get a really good monitor with hight resolution and maybe 27" so the graphics card needs to be able to make best use of that. So a few questions 1) Is the bottle neck in performance mostly still the harddrives? 2) Aren't most processors e.g. i5 etc even i3 so far a head of other bottlenecks it makes litte difference the higher you go. Isn't the Graphics card dealing with heavy graphics so what really slows because of a slow CPU? So from this my thinking is to get a SSD drive as my primary drive for OS etc and have loads of memory e.g. 6-8GB and a decent mid level graphics card? It doesn't seem at my level worth spending much on CPU and any other parts really. I basic parts off the top of my head Case, Motherboard CPU SSD Drive SATA Drive Power Supply Memory Cooling (fan?) Graphics Card Network Card Keyboard DVD drive Mouse Windows Monitor Am I missing anything? Any helpful tips or general education much appreciated. Thanks, Derek

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  • Probability of Blade Chassis Failure

    - by ChrisZZ
    In my organisation we are thinking about buying blade servers - instead of rack servers. Of course technology vendors also make them sound very nice. A concern, that I read very often in different forums, is, that there is a theoretical possibility of the server chassis going down - which would in consequence take all the blades down. That is due to shared infrastructure. My reaction on this probability would be to have redundancy and by two chassis instead of one (very costly of course). Some people (including e.g. HP Vendors) try to convince us, that the chassis is very very unlikely to fail, due to many redundancies (redundant power supply, etc.). Another concern on my side is, that if something goes down, spare parts might be required - which is difficult in our location (Ethiopia). So I would ask to experienced administrators, that have managed blade server: What is your experience? Do they go down as a whole - and what is the sensible shared infrastructure, that might fail? That question could be extended to shared storage. Again I would say, that we need two storage units instead of only one - and again the vendors say, that this things are so rock solid, that no failure is expected. Well - I can hardly believe, that such a critical infrastructure can be very reliable without redundancy - but maybe you can tell me, whether you have successfull blade-based projects, that work without redundancy in its core parts (chassis, storage...) At the moment, we look at HP - as IBM looks much to expensive... thanks a lot best regards Christian

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  • Exchange MSExchangeIS Mailbox Store Error

    - by Bart Silverstrim
    Boss asked me to check to see if I could figure out why he's had to restart the services on the Exchange server three mornings in a row now. While going through the system logs I ran across an error from the MSExchangeIs Mailbox Store, category General, Event 9690. The message said (edited to make generalized): Exchange store 'First Storage Group\Mailbox Store (Servername)': The logical size of this database (the logical size equals the physical size of the .edb file and the .stm file minus the logical free space in each) is 22GB. This database size has exceeded the size limit of 22 GB. This database will be dismounted immediately. Hmm...happened at five in the morning, and I'm thinking this is a pretty good hint that this leads to the culprit. Thing is I'm not an Exchange expert, so I'm still googling around to figure out how to fix the problem. Any better guidance out there? Or am I barking up the wrong binary tree? Exchange System Manager reports that the server is "version 6.5 build 7638.2, SP2", standard, which I believe is Exchange 2003. It's running on Windows Server 2003 R2 Standard, SP2.

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  • Client certificate based encryption

    - by Timo Willemsen
    I have a question about security of a file on a webserver. I have a file on my webserver which is used by my webapplication. It's a bitcoin wallet. Essentially it's a file with a private key in it used to decrypt messages. Now, my webapplication uses the file, because it's used to recieve transactions made trough the bitcoin network. I was looking into ways to secure it. Obviously if someone has root access to the server, he can do the same as my application. However, I need to find a way to encrypt it. I was thinking of something like this, but I have no clue if this is actually going to work: Client logs in with some sort of client certificate. Webapplication creates a wallet file. Webapplication encrypts file with client certificate. If the application wants to access the file, it has to use the client certificate. So basically, if someone gets root access to the site, they cannot access the wallet. Is this possible and does anyone know about an implementation of this? Are there any problems with this? And how safe would this be?

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  • Redis as substitution for Memcache

    - by Boban P.
    We have distributed web app, and for now, as session handler, we use two separate instances of memcache in redundancy, so everything that is written in one memcache is also written in other. Memcache is fairly easy to install, use, and maintain but we have one problem: if one memcache fail, everything is fine, php comunicate with other instance which has all data (although, half of connections have a delay because they try to use failed one, wait a little, and then contact other memcache). When failed instance comes back to life again, it starts up empty. If established session request data from that instance, session fails, and user logs out, and that happens to half of users.So, we are thinking about to switch to redis for session handling, and maybe keep memcache for cache only. My questions are: If we setup redis instances as master-slave, and if master fails, can sentinel promote slave as new master and when old master comes back to life, will it stay as slave or not? Is redis call malloc at startup to allocate part of memory, like memcache or varnish, or it calls malloc for every key inserted? And what are pros and cons of that?

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  • Is encryption really needed for having network security? [closed]

    - by Cawas
    I welcome better key-wording here, both on tags and title. I'm trying to conceive a free, open and secure network environment that would work anywhere, from big enterprises to small home networks of just 1 machine. I think since wireless Access Points are the most, if not only, true weak point of a Local Area Network (let's not consider every other security aspect of having internet) there would be basically two points to consider here: Having an open AP for anyone to use the internet through Leaving the whole LAN also open for guests to be able to easily read (only) files on it, and even a place to drop files on Considering these two aspects, once everything is done properly... What's the most secure option between having that, or having just an encrypted password-protected wifi? Of course "both" would seem "more secure". But it shouldn't actually be anything substantial. I've always had the feeling using any kind of the so called "wireless security" methods is actually a bad design. I'm talking mostly about encrypting and pass-phrasing (which are actually two different concepts), since I won't even consider hiding SSID and mac filtering. I understand it's a natural way of thinking. With cable networking nobody can access the network unless they have access to the physical cable, so you're "secure" in the physical way. In a way, encrypting is for wireless what building walls is for the cables. And giving pass-phrases would be adding a door with a key. So, what do you think?

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  • Getting old bluetooth headset out of standby on Windows 7

    - by luagh45
    I think this is the problem, and if not, I'm open to suggestions. I have an old Jabra BT200 that I used to use on my phone. When a phone call was coming in it would beep using its own noises (meaning the phone never rang inside the headset) and then I could push the 'answer/hang up' button and sound and mic would start working. I have now paired it with Windows 7, and it looks good. Under the playback menu I have 'Bluetooth Hands free Audio / Jabra BT200 (Mono Audio) / Ready', and under the recording menu I have 'Bluetooth Audio Input Device / Jabra BT200 (Mono Audio) / Ready'. However when I try to test the speakers Windows sends a sound, but I never hear it, and when I talk in the mic, Windows never hears me. If I right click either the Bluetooth mic or speakers there's an option to 'Connect', but it's grayed out and I cannot click it. As the final piece of knowledge I have, my headset blinks once every 3 seconds when it's in standby and I can't get that to change. If everything was working it should blink once every second at which point I think all of my problems would be fixed. Hence my issue: I can't seem to get my headset out of standby. On my headset I've tried sending it test noises and then pressing the 'Answer' button, but still nothing. The headset beeps when I press it, so it works, it just doesn't ever come out of standby. Is there maybe some way to trick my headset into thinking it's getting a phone call from my computer?

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  • Measure Total Bandwidth for Billing

    - by TonyZ
    I am setting up a new network which customers will host their applications on. It needs to be able to scale out to a few hundred servers and each server will have several VMs on it. Right now in my test environment, after the telco router, we are using a Linux router/firewall which is then connected to a Layer 2 switch. Could be a layer 3 in the future. I need to track total bandwidth per VM for each machine, and I need to do it in a way that it is not part of the VM. Each VM will have a private class ip address which is Natted by the gateway, or we may eventually run more than firewall/reverse proxy off a layer 3 switch. So my thinking is that I can do it off of a promiscuous port on the switches, or at the gateway firewall. I would like to have an out of the box solution, preferably open source. Does anyone have suggestions on the easiest way to set this up, and the easiest tool to use. I have looked at the web sites for Nagios, Zenoss, Zabbix, ntops on the firewall, etc. It is hard to ascertain just from the web sites if they do exactly this or not. Obviously, performance is also somewhat key here. Anything running on the gateway should not drag it down doing traffic accounting. Thanks for any thoughts. Tony Zakula

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  • Configure tomcat behind loadbalancer to respond on HTTP and HTTPS

    - by user253530
    I have 2 tomcat machines behind a load balancer on Amazon EC2. Until now The load balancer was configured to respond only on https. So in order to access our services you would go to https://url. Tomcat was configured to listen on 8080 but the connector had additional params that would tell tomcat that it is behind a proxy and that it should respond on HTTPS 443. The connector looks like this: <Connector scheme="https" secure="true" proxyPort="443" proxyHost="my.domain.name" port="8080" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8443" useBodyEncodingForURI="true" URIEncoding="UTF-8" /> What i would like to do is to open port 80 on the load balancer and basically allow traffic on HTTP and HTTPS. I've configured the load balancer to redirect all HTTP traffic to the tomcat machines on port 8088. I was thinking that i could define a new connector so that all HTTPS traffic goes to 8080 and HTTP to 8088. Unfortunately i did not succeed. Here is my connector <Connector port="8088" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8443" useBodyEncodingForURI="true" URIEncoding="UTF-8" /> Am I missing something? Thanks

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  • How would I setup iMail to forward a user's mail to another service w/o leaving a copy locally?

    - by Scott Mayfield
    I have an iMail 2006 server installation in which I have a particular user that has several aliases that all point to a single user (me, for the record). I've been copying all of my mail to GMail and reading it there, but it annoys me that I have to go back weekly and log into my mail account on iMail and delete between 6 and 10 thousand copies of messages I've already received, in order to keep my mailbox from filling up (yes, I have it set with no quota, but I consider it bad form to just let the box grow indefinitely). I've got the copying setup via an inbound user rule, but I'm wondering how to accomplish a "copy and delete" rule. The manual isn't clear on what happens with multiple matching rules (will they be processed in order, or is it a first match situation?) and there isn't a means to combine multiple actions into a single rule. If I use the "forward" action, I THINK that it's going to screw up all the sender information once the mail reaches my GMail account and show it as coming from me instead of the original senders (can anyone confirm that this is accurate?) An easy answer would be to delete my user account entirely, replace it with an alias that maps to my GMail account, but then I would lose my ability to log into the system for admin duties. So that leads me to creating a second, lesser known account for admin use, but since it's a real account, sooner or later I'm going to get mail sent to it and I'll be back to the same situation of having a user account that doesn't get emptied periodically. I imagine I can set the quota to 0 MB to cause all incoming mail to my admin account to bounce, or setup an inbound rule to bounce everything, but this is starting to sound kludgy to me. Does anyone know of a more direct work around to copying a user's incoming mail to an outside server and then deleting the local copy w/o removing their account entirely? Or is this just wishful thinking?

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  • Home media storage solution

    - by Dan
    I record lots of personal HD film footage and am looking for a cheap way to store all of this. I take ~120 GB of footage each month, so something expandable would be nice... something that might be able to hold 6+ SATA drives. There is a low load requirement, as there is never more than a user or two... but it should be able to keep up with streaming 2 simultanious HD videos. I don't really want to spend more than $200-$300 on top of the $900 I am thinking of spending for 6X2GB SATA drives@ $150 apiece, but I am willing to pay extra for a quality solution. Should I get a cheap NAS server? a cheap multi-drive external enclosure? should I just get some used systems off craigslist? If it is an independent system I'll probably just throw ubuntu on it since I can maintain that well. Its easy to do a software raid from ubuntu too, if I choose to go that way. Thanks

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  • Piecing together low-powered hardware for an RS-232 terminal server

    - by Fred
    I'm working on reconstructing my Cisco lab for training/educational purposes and I found that the actual terminal server I have is dead. I have a couple of 8-port PCI serial cards which would be more than ample for my lab, but I don't want to leave my personal computer running to be able to access the console ports. Ideally I would access the terminal server remotely, either by SSH/RDP to the box (depending on what OS I go with) or by installing a software package that allows me to telnet directly to a serial port. I know I've found a program that does this under Linux in the past but its name escapes me at the moment. I'm thinking about scavenging for some old hardware, on eBay or something, to put together a low-powered PC. Needs to be something that: Has Low-power consumption Has at least 2 PCI slots (though I certainly wouldn't complain about having more) Has onboard Ethernet (or, if not, another PCI or ISA slot (not shared)) Can be headless once an OS installed (probably Linux) I'm currently leaning towards an old fashioned Pentium (sub-133MHz era) but I am wondering if anybody else knows of another platform/mobo that would suit these needs. Alternatively, I've been considering buying a Raspberry Pi and a big USB hub along with a bunch of USB-Serial adapters but this sounds like it'd get messy quick with cables and adapters all over the place, and I may not even have the same ttyS#'s between boots.

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  • How to choose the most optimal RAID settings on PE2950

    - by javano
    I have some Dell PowerEdge 2950's with 4x 15k, 150GB Cheetah SAS drives in them. They are going to be VM hosts, CentOS running ESXi with Windows Server 2k8 guests. Some guests will be hosting IIS servers, and others MSSQL servers. I am trying to set the RAID virtual disks settings and can't decide which is more optimal given this situation; Read Policy: Out of Read-Ahead, No-Read-Ahead and Adaptive Read-Ahead, the default is Read-Ahead. I will be making large sequential writes initially, writing out blank images for virtual machine hard drives (lets say 30GBs from /dev/zero for example) so Read-Ahead seems good at first. But within the virtual machines reads could be random from anywhere within their file systems as they are IIS and MSSQL servers, so perhaps No-Read-Ahead is a better idea? Now I think Adaptive Read-Ahead would be better then as a compromise but I don't know much about this option, how does it compare in performance to the others? Write Policy: write-back caching, write-through caching, the default is write-back caching. The default of write-back caching is safer than write-through caching but at a performance expense. My thinking here is that in the event of power loss for example, it seems more likely in my head (this is why I need some clarification!) that damage will occur to a guest VM with write-back caching enabled, so I should favour write-through? I have searched around and there is obviously no definitive answer, so I would like to find out what is best for my situation.

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  • Serving and caching content from Amazon S3 with Tomcat

    - by Rob
    Hi all, We're looking to serve a range of content using Amazon S3 as a store for the content and Tomcat to host the web application. The content is divided into free and paid for content. We intend to authenticate the users when they access the web application running in Tomcat. Based around their authentication we are able to tell if the user has access to paid for content or simply free stuff. So I envision the flow of a request being something like this: Authenticated request to Tomcat If user is "paid" user, display links to premium content Direct requests for paid content back through Tomcat to prevent direct access to it by non-paying users. Tomcat makes request to S3 through a web cache to keep our costs down Content is returned to user. As we have to pay for each request to S3, I'd ideally like to cache content locally to the Tomcat instance after it has been requested for the first time to keep costs to a minimum and to speed things up. I would also like to be able to invalidate this cache if we publish fresh content to S3. So to confirm my proposal: Client Request - Tomcat - Web Cache - S3 To invalidate the cache, I was thinking of using something like PubSubHubbub with the cache waiting for updates to the feed for content that it should invalidate. I'd appreciate some general feedback on this approach as I've no real experience of caching and I'm sure I've made some invalid assumptions. I'd also appreciate any recommendations for caching technologies. Thanks.

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  • How do I calculate clock speed in multi-core processors?

    - by NReilingh
    Is it correct to say, for example, that a processor with four cores each running at 3GHz is in fact a processor running at 12GHz? I once got into a "Mac vs. PC" argument (which by the way is NOT the focus of this topic... that was back in middle school) with an acquaintance who insisted that Macs were only being advertised as 1Ghz machines because they were dual-processor G4s each running at 500MHz. At the time I knew this to be hogwash for reasons I think are apparent to most people, but I just saw a comment on this website to the effect of "6 cores x 0.2GHz = 1.2Ghz" and that got me thinking again about whether there's a real answer to this. So, this is a more-or-less philosophical/deep technical question about the semantics of clock speed calculation. I see two possibilities: Each core is in fact doing x calculations per second, thus the total number of calculations is x(cores). Clock speed is rather a count of the number of cycles the processor goes through in the space of a second, so as long as all cores are running at the same speed, the speed of each clock cycle stays the same no matter how many cores exist. In other words, Hz = (core1Hz+core2Hz+...)/cores.

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  • How would I setup iMail to forward a user's mail to another service w/o leaving a copy locally?

    - by Scott Mayfield
    I have an iMail 2006 server installation in which I have a particular user that has several aliases that all point to a single user (me, for the record). I've been copying all of my mail to GMail and reading it there, but it annoys me that I have to go back weekly and log into my mail account on iMail and delete between 6 and 10 thousand copies of messages I've already received, in order to keep my mailbox from filling up (yes, I have it set with no quota, but I consider it bad form to just let the box grow indefinitely). I've got the copying setup via an inbound user rule, but I'm wondering how to accomplish a "copy and delete" rule. The manual isn't clear on what happens with multiple matching rules (will they be processed in order, or is it a first match situation?) and there isn't a means to combine multiple actions into a single rule. If I use the "forward" action, I THINK that it's going to screw up all the sender information once the mail reaches my GMail account and show it as coming from me instead of the original senders (can anyone confirm that this is accurate?) An easy answer would be to delete my user account entirely, replace it with an alias that maps to my GMail account, but then I would lose my ability to log into the system for admin duties. So that leads me to creating a second, lesser known account for admin use, but since it's a real account, sooner or later I'm going to get mail sent to it and I'll be back to the same situation of having a user account that doesn't get emptied periodically. I imagine I can set the quota to 0 MB to cause all incoming mail to my admin account to bounce, or setup an inbound rule to bounce everything, but this is starting to sound kludgy to me. Does anyone know of a more direct work around to copying a user's incoming mail to an outside server and then deleting the local copy w/o removing their account entirely? Or is this just wishful thinking? Thanks in advance. Scott

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  • Using UDF on a USB flash drive

    - by CesarB
    After failing to copy a file bigger than 4G to my 8G USB flash drive, I formatted it as ext3. While this is working fine for me so far, it will cause problems if I want to use it to copy files to someone which does not use Linux. I am thinking of formatting it as UDF instead, which I hope would allow it to be read (and possibly even written) on the three most popular operating systems (Windows, MacOS, and Linux), without having to install any extra drivers. However, from what I found on the web already, there seem to be several small gotchas related to which parameters are used to create the filesystem, which can reduce the compability (but most of the pages I found are about optical media, not USB flash drives). I would like to know: Which utility should I use to create the filesystem? (So far I have found mkudffs and genisoimage, and mkudffs seems the best option.) Which parameters should I use with the chosen utility for maximum compability? How compatible with the most common versions of these three operating systems UDF actually is? Is using UDF actually the best idea? Is there another filesystem which would have better compatibility, with no problematic restrictions like the FAT32 4G file size limit, and without having to install special drivers in every single computer which touches it?

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