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• Which topics do I need to research to enable me to complete my self-assigned "Learning Project"?

  - by Anonymous -

  I want to continue learning C#. I've read parts of a few books recommended on here and the language is feeling more familiar by the day. I'd like to tackle a mid-sized personal project to take my expertise to the next level. What I'd like to do, is create an application that 'manages expenses', that runs on multiple machines on a LAN. So for example, say we have person1 and person2 on seperate machines running the application, when person1 enters an expense, it will appear on person2's (pretty UI) view of the expenses database and vice versa. What topics do I need to research to make this possible for me? I plan on learning WPF for the UI (though the steep learning curve (or so I'm told) has me a little anxious about that at this stage. With regards to the database, which database would you recommend I use? I don't want a 'server' for the database to run on, so do I need to use an embedded database that each client machine runs a copy of that updates to each other (upon startup/entering of expense on any machine etc)? What topics under networking should I be looking at? I haven't studied networking before in any language, so do I need to learn about sockets or?

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• Should I avoid or embrace asking questions of other developers on the job?

  - by T.K.

  As a CS undergraduate, the people around me are either learning or are paid to teach me, but as a software developer, the people around me have tasks of their own. They aren't paid to teach me, and conversely, I am paid to contribute. When I first started working as a software developer co-op, I was introduced to a huge code base written in a language I had never used before. I had plenty of questions, but didn't want to bother my co-workers with all of them - it wasted their time and hurt my pride. Instead, I spent a lot of time bouncing between IDE and browser, trying to make sense of what had already been written and differentiate between expected behavior and symptoms of bugs. I'd ask my co-workers when I felt that the root of my lack of understanding was an in-house concept that I wouldn't find on the internet, but aside from that, I tried to confine my questions to lunch hours. Naturally, there were occasions where I wasted time trying to understand something in code on the internet that had, at its heart, an in-house concept, but overall, I felt I was productive enough during my first semester, contributing about as much as one could expect and gaining a pretty decent understanding of large parts of the product. I was wondering what senior developers felt about that mindset. Should new developers ask more questions to get to speed faster, or should they do their own research for themselves? I see benefits to both mindsets, and anticipate a large variety of responses, but I figure new developers might appreciate your answers without thinking to ask this question.

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• Is it possible to use two different ErrorDocuments for different paths of a website?

  - by tapwater

  this is my first question on stackexchange and it might be a bit confusing. I currently run PmWiki (sorry, you'll have to google it, new user can only have 2 hyperlinks) at mydomain.com/pmwiki. I have a 404 page and .htaccess set up in my site's document root for 404 pages regarding anything that doesn't have to do with my wiki. By default, PmWiki handles URLs a little confusingly so I had to use this in order to get it to look like mydomain.com/pmwiki/Namespace/Page I had to create a .htaccess in /pmwiki to remove parts of the URL. PmWiki also has a custom 404 (Site/PageNotFound) page that has stopped working, now my site uses the /404.htm page. I noticed this when trying to install this "recipe" to enable case-insensitive URLs. Currently the only way to access Site/PageNotFound is by actually linking to it, and, if you read how that recipe seems to function, this is an issue. Currently mydomain.com/pmwiki/blahblah and mydomain.com/pmwiki/legitimate_namespace_but_lowercase/legitimate_lowercase_page_name both direct to mydomain.com/404.htm. I have to admit I'm very confused, and I apologize if I was unclear in any of this, but I could definitely use some help. Thanks!

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• Internal Libraries (Subversion Externals, 'library' branch, or just another folder)

  - by Ntsc

  Currently working on multiple projects that need to share internal libraries. The internal libraries are updated continually. Currently only 1 project needs to be stable but soon we will need to have both projects stable at any given time. What is the best way to SVN internal libraries? Currently we are using the 'just another folder' like so... trunk\project1 trunk\project2 trunk\libs It causes a major headache when a shared library is updated for project1 and project2 is now dead until the parts that use the library are updated. So after doing some research on SVN externals I thought of this... trunk\project1\libs (external to trunk\libs @ some revision) trunk\project2\libs (external to trunk\libs @ different revision) trunk\libs\ I'm a little worried about how externals work with commits and not making library commits so complicated that I am the only one capable of doing it (mostly worried about branches with externals as we use them extensively). On top of that we have multiple programming languages within each project some of which don't support per-project library directories (at least not easily) so we would need to check out on a per project basis instead of checking out the trunk. There is also the 'vendor' style branching of libraries but it has the same problem as above where the library would have to be a sub folder of each project and is maybe a little to complicated for how little projects we have. Any insight would be nice. I've spent quite a bit of time reading the Subversion book and feeling like I'm getting no where.

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• How to avoid being fooled

  - by Dacav

  I'm a big fan of the OpenSource development model, and I think that sharing information, knowledge and ideas is the best way of working in software development. Still I think that being hired for proprietary software development must not be demonized. Of course, as there's a no reward in terms of sharing there must be a bigger reward in terms of money (i.e. I surrender all my rights for cash). It may happen that one gets hired piecework, for a single project: in this case one is more vulnerable to dishonest employers. This didn't happen to me personally, but some friends of mine had bad experiences, and lost a lot of time without being fairly retributed. Of course a contract should protect both parts. But contracts can be very generic in the specification. Software is not anything but a palpable good! Besides I don't think that contracts can distinguish between a well written software and a poorly written one. Note also that, in this (nasty) spirit, it's also likely that the employer cannot trust the employee! So also the employer should be protected by a dishonest employee). My question is the following: Which is, in your opinion, a good way of avoiding this kind of situation from the technical perspective?

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• SDL blitting multiple surfaces at once

  - by extropic_engine

  I'm trying to write a platforming game where the sprites for the level backgrounds are broken up into 512x512 chunks. I keep 3 chunks in memory at a time and I'm trying to write code to blit all three to the screen. Here is the current code I have: SDL_Rect where; where.y = -game->camera->y; where.x = -game->camera->x - MAP_WIDTH; SDL_BlitSurface(left_chunk, NULL, screen, &where); where.x = -game->camera->x; SDL_BlitSurface(center_chunk, NULL, screen, &where); where.x = -game->camera->x + MAP_WIDTH; SDL_BlitSurface(right_chunk, NULL, screen, &where); The issue I'm running into is that whichever chunk gets blitted first is the only one that shows up. The rest fail to appear onscreen. I think the issue might have something to do with alpha transparency, but even if the chunks don't overlap at all they still fail to blit. In other parts of the code I'm blitting multiple things to the screen at once, such as characters and backgrounds, and they all show up correctly. This particular segment of code is the only area I'm encountering this problem. If I comment out the line that blits left_chunk, it changes to this:

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• Problem with understanding how to start

  - by Coolface

  Okay, this might be a little off-topic but i try anyway. Sorry to bother. So i'm working as sysadmin for at least 5 years now and i quite enjoy IT field in general. Somehow i was never interested in programming much but always want to learn something at least easy and for personal usage. As sysadmin i need scripting skills so learn shell scripting without much problems, i also try to learn pascal, delphi, basic over time and must recent was python. Well, my problem is when i try to learn programming i just can't apply what i learn from the books to the real word. What i mean is i understand there are data structures, algorithms, variables, lib's, if-then logic, etc. but i just can't understand how to apply this things when i want to do real things. Like i want to get a something simple as parse web page, i draw a quick algorithm like get a web page, find a word on it and write a to file, on the paper everything look simple but when i get to the coding i just stuck pretty much from the start. I try read code of the real programs that just totally confusing especially big parts with many classes so i'm just quickly lost a trail what this code do. I think i just lack some fundamentals to see a big picture but don't really know what this might be? Or maybe i just don't have a passion to programming at all... My best bet was a shell scripting so i have really no problems to write complex scripts but this just not enough. Recently i was read around 5 or 6 python books because everyone say it's so easy even kid can code something but still no much luck, python is good and easy but i can't make something harder then a prodecurial style code like in bash for easy things but when i want harder things i'm still stuck. In college i was also not a math and tech guy and like to study non-tech stuff mostly like economy, psychology maybe that my problem? Anyway any advice would be greatly appriciated.

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• Where do I read more about building an architecture like Google has? [on hold]

  - by user107148

  I want to develop a program that watches and traverses a rather big network for data. This data should then be available to search through with my program, maybe through a web interface or something. My intuitive thought at the moment is to build an architecture kind of like the one Google has. One "front-end" (the Google Search page) which is essentially a regular web application and one "back-end" (which in Google's case traverses the web). Now for the hard part: If I decide to make such a system, how should communication be done between these parts? One idea I had is to use some kind of database that both the back-end and front-end can access, but then comes the issues of concurrent writes and reads. Another issue with just using a database to communicate is that it makes it hard to "notify" the other part when something changes. Let's say that I want the "front-end" part to push changes to the UI when a change is noticed in the back-end. Then the back-end would have to have some way of notifying the front-end of this.

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• Interfaces: profit of using

  - by Zapadlo

  First of all, my ubiquitous language is PHP, and I'm thinking about learning Java. So let me split my question on two closely related parts. Here goes the first part. Say I have a domain-model class. It has some getters, setters, some query methods etc. And one day I want to have a possibility to compare them. So it looks like: class MyEntity extends AbstractEntity { public function getId() { // get id property } public function setId($id) { // set id property } // plenty of other methods that set or retrieve data public function compareTo(MyEntity $anotherEntity) { // some compare logic } } If it would have been Java, I should have implemented a Comparable interface. But why? Polymorphism? Readbility? Or something else? And if it was PHP -- should I create Comparable interface for myself? So here goes the second part. My colleague told me that it is a rule of thumb in Java to create an interface for every behavioral aspect of the class. For example, if I wanted to present this object as a string, I should state this behaviour by something like implements Stringable, where in case of PHP Stringable would look like: interface Stringable { public function __toString(); } Is that really a rule of thumb? What benefits are gained with this approach? And does it worth it in PHP? And in Java?

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• Updating to linux-image-3.2.0-26-generic occupies all disk space

  - by user42228

  I just ran a normal update through the update manager that wanted to update me to linux-image-3.2.0-26-generic. The installation paused halfway with a message that the root was full. I checked the disk usage, and noticed that one of the newly installed files: /lib/modules/3.2.0-26-generic/modules.ccwmap took up 63GB(!). Compared to the previous version: /lib/modules/3.2.0-24-generic/modules.ccwmap that took up only 4KB it seems like something went awfully wrong! As mentioned the update was paused when i ran out of disk space. There is no option in the update dialog to cancel or perform rollback on the update. Is it asking for trouble to kill the update manager? Any ideas as to what went wrong, and what I can do to remedy it? It's only minimal how much space I can free on that partition (without deleting the above mentioned file). If it is any help, the update was paused after this: Examining /etc/kernel/postinst.d. run-parts: executing /etc/kernel/postinst.d/dkms 3.2.0-26-generic /boot/vmlinuz-3.2.0-26-generic

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• Batch print, reprint and scan

  - by Nikita K. Tsarov

  I am using ubuntu 13.10 with Epson wireless scanner/printer/fax WF 2540(It has an automatic document feeder- ADF). What I am trying to achieve is to be able to print with confidence over already populated A4 pages(hand drawn or otherwise). The idea is to get a batch of A4 pages grouped in a particular order and have them batch printed on specific parts of each page ,viewed on screen and edit/processed page by page. My idea was to batch scan the documents in order and display each scanned page to use that to judge/fit on-screen the coordinates for the output of each pages image... The easiest way to explain this is to look at these slide : https://drive.google.com/file/d/0B0Kuhf6iBidTNUl3U1NtT0pGbnc/edit?usp=sharing I would like to have this automated as much as possible using this printer but I am open to other suggestions. Are there any other better printers that can automatically scan and print at the document that is being scanned...with an accurate positioning in relation to elements already printed on the page?? Are there any other forums I should be asking and looking for answer/suggestions on my case/dilema??

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• Upgraded from ubuntu 12.04 to 12.10 issues

  - by ubuntu novice user

  I recently upgraded 12.04 to 12.10 ubuntu and then all hell broke loose. Being more specific, I have a Compaq machine and its hard disk is partitioned into 3 parts, so when I installed Ubuntu 10.04, I installed it in windows, since then have upgraded with each new ubuntu release via the update manager without any problems. I have installed the 64 bit versions. 12.10 downloaded via update manager, and initial downloading of packages was without problems, however, as it tried to install the packages, error messages appeared. The first was one about missing lib files, but I clicked to continue, since I am a relative novice on ubuntu. It continued, and during the restart process, when it was powering down, the computer hanged on the shutting down bit without rebooting for more than half an hour, so I manually shut down the machine and restarted it. Then a new error message appeared stating could not find disk, and I hit the manual fix option, and it now boots to an empty ubuntu desktop with my wallpaper but no launcher and the graphics appears as if this was put on a 640 x 480 resolution, and the screen no longer fits onto my 19" LCD. I had to use Ctrl-Alt-T to log out and then restart from there. How can I resolve this issue. Please help!

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• Some DHCP clients end up with wrong DNS server

  - by Nic Waller

  The scenario: DC running Windows Server 2008 R2 providing DNS + DHCP Cisco 1811 Router as the gateway 30 Windows XP DHCP clients on the LAN The problem: Some workstations are spontaneously switching to an incorrect DNS server. Specifically, ipconfig /all shows that they start using the gateway as a DNS server. This happens about 5-10 times a day to various computers, sometimes more than once per day. The workaround: Repairing the connection on the XP client always fixes the problem, and the correct DNS server address is obtained. We lost our main DNS/DHCP machine a week ago, and had to bring this one online as a spare. We've been having this issue since then. DHCP leases on the old and new servers are configured for "wired" (8 day) duration. There are definitely no other DHCP servers active on the LAN. So far there is no discernible pattern about which clients will show this problem, or when. When I ran DCDIAG /test:DNS it came back clean. Manual inspection of the DNS zone shows that all the records are appearing as expected, with no traces of the previous machine in there. Update Feb 27: Added screenshots. Here is a screenshot of the DHCP scope options on the 2008 R2 server. And here is a screenshot of ipconfig /all running on a healthy host. I don't have any ailing hosts at the moment, but will grab a screencap next time it happens. Update Feb 28: More screenshots. Here's a screenshot of DHCP and DNS traffic from a healthy client when repairing the local area connection. There's definitely only one server responding, but it does seem strange that the negotiation takes place twice. I'll try to get a similar capture from a sick machine this coming week. Update Mar 01: Caught a bad ipconfig. Here's a screenshot of ipconfig /all from a client that had this issue. It says the lease was issued this morning, but it doesn't even have an entry for the secondary DNS I set up yesterday. Both DNS servers were discovered properly when repairing the connection. Update Mar 01: It even got the sysadmin! This issue finally affected my personal workstation this morning. Unfortunately I had just rebooted and wasn't running a packet dump at the time. I set up a secondary server yesterday, and was logging all DNS traffic to it. My machine had not contacted the secondary DNS in over half an hour, so that says to me that it's just spontaneously reverting to the gateway without even failing over to secondary DNS first. Today I swapped the order of the DNS servers in DHCP, so the secondary is primary and vice versa. I will update again once I know how that goes.

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• Splitting an internet connection between multiple separate subnetworks

  - by pythonian4000

  Problem I have an internet connection that I want to split between four separate networks. My requirements are: I need to be able to monitor the amount of bandwidth and data being used by each network, and notify or control as necessary. The four networks should only be able to connect to the internet, not each other. My parents need to be able to operate it, so it needs a simple, preferably Windows-based GUI. Progress so far Server I have a mini-ITX server with six Gigabit ethernet ports - one for the ethernet internet connection, one for each of the four networks, and one for remote access to the server for administration. Bandwidth control I spent a long time researching solutions here. The majority of the control systems/software I found could control bandwidth usage via QOS, but could not monitor or control the amount of data being used. Eventually I found the SoftPerfect Bandwidth Manager, which has everything I need in terms of monitoring and control - per-interface quota management, usage statistics, a web interface for checking usage, and email notifications when quotas are exceeded. It is also Windows-based and has a simple GUI. Internet sharing This is where I am having issues. I am currently using Windows XP Pro SP2 for the server (yes, I know this is far from ideal, but it's the only spare Windows OS I currently have). I can't use the built-in Internet Connection Sharing for several reasons: The upstream internet router has an IP of 192.168.0.1 which ICS clashes with, and I cannot change the router settings. ICS can only share an internet connection with a single interface, but I have four. I have tried bridging the four network cards, but then the Bandwidth Manager cannot see the four individual interfaces - it only sees the bridge. I have tried setting up Dual DHCP DNS server (and am having issues getting DHCP offers to be received by clients), but that would still require gateway software of some sort, which I have been unable to find. My current attempt is to use OpenVPN, with a server for the internet NIC and a separate client for each of the four networks. My thought is that I could bridge the OpenVPN TAP devices to each NIC, meaning that the Bandwidth Manager would control traffic from the bridge instead of the interface. I have not made much progress here though - I've never used OpenVPN before. Questions Is there a Windows software package that does everything I need? (Unlikely, I know) Is there a Windows software package that will share internet between multiple NICs without bridging? Are either of my about attempts feasible? Would it help to have a newer/server version of Windows? Is there a non-Windows alternative that is easy to use?

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• Quantifying the effects of partition mis-alignment

  - by Matt

  I'm experiencing some significant performance issues on an NFS server. I've been reading up a bit on partition alignment, and I think I have my partitions mis-aligned. I can't find anything that tells me how to actually quantify the effects of mis-aligned partitions. Some of the general information I found suggests the performance penalty can be quite high (upwards of 60%) and others say it's negligible. What I want to do is determine if partition alignment is a factor in this server's performance problems or not; and if so, to what degree? So I'll put my info out here, and hopefully the community can confirm if my partitions are indeed mis-aligned, and if so, help me put a number to what the performance cost is. Server is a Dell R510 with dual E5620 CPUs and 8 GB RAM. There are eight 15k 2.5” 600 GB drives (Seagate ST3600057SS) configured in hardware RAID-6 with a single hot spare. RAID controller is a Dell PERC H700 w/512MB cache (Linux sees this as a LSI MegaSAS 9260). OS is CentOS 5.6, home directory partition is ext3, with options “rw,data=journal,usrquota”. I have the HW RAID configured to present two virtual disks to the OS: /dev/sda for the OS (boot, root and swap partitions), and /dev/sdb for a big NFS share: [root@lnxutil1 ~]# parted -s /dev/sda unit s print Model: DELL PERC H700 (scsi) Disk /dev/sda: 134217599s Sector size (logical/physical): 512B/512B Partition Table: msdos Number Start End Size Type File system Flags 1 63s 465884s 465822s primary ext2 boot 2 465885s 134207009s 133741125s primary lvm [root@lnxutil1 ~]# parted -s /dev/sdb unit s print Model: DELL PERC H700 (scsi) Disk /dev/sdb: 5720768639s Sector size (logical/physical): 512B/512B Partition Table: gpt Number Start End Size File system Name Flags 1 34s 5720768606s 5720768573s lvm Edit 1 Using the cfq IO scheduler (default for CentOS 5.6): # cat /sys/block/sd{a,b}/queue/scheduler noop anticipatory deadline [cfq] noop anticipatory deadline [cfq] Chunk size is the same as strip size, right? If so, then 64kB: # /opt/MegaCli -LDInfo -Lall -aALL -NoLog Adapter #0 Number of Virtual Disks: 2 Virtual Disk: 0 (target id: 0) Name:os RAID Level: Primary-6, Secondary-0, RAID Level Qualifier-3 Size:65535MB State: Optimal Stripe Size: 64kB Number Of Drives:7 Span Depth:1 Default Cache Policy: WriteBack, ReadAdaptive, Direct, No Write Cache if Bad BBU Current Cache Policy: WriteThrough, ReadAdaptive, Direct, No Write Cache if Bad BBU Access Policy: Read/Write Disk Cache Policy: Disk's Default Number of Spans: 1 Span: 0 - Number of PDs: 7 ... physical disk info removed for brevity ... Virtual Disk: 1 (target id: 1) Name:share RAID Level: Primary-6, Secondary-0, RAID Level Qualifier-3 Size:2793344MB State: Optimal Stripe Size: 64kB Number Of Drives:7 Span Depth:1 Default Cache Policy: WriteBack, ReadAdaptive, Direct, No Write Cache if Bad BBU Current Cache Policy: WriteThrough, ReadAdaptive, Direct, No Write Cache if Bad BBU Access Policy: Read/Write Disk Cache Policy: Disk's Default Number of Spans: 1 Span: 0 - Number of PDs: 7 If it's not obvious, virtual disk 0 corresponds to /dev/sda, for the OS; virtual disk 1 is /dev/sdb (the exported home directory tree).

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• Troubleshooting major performance issue: Is culprit Intel RST, Hard drive, or something else?

  - by Sean Killeen

  The Setup I have the following components that come into play in this situation: ASUS P8Z68 V/PRO motherboard a RAID1 configuration (1x 1TB drive, 1 x 2TB drive -- I explain below), accelerated with an SSD using Intel's RST software, and 1 TB drive standing by as a spare. Core i7 2600k 32 GB RAM Windows 8.1 This box was designed to be beast, and until just recently, was very good at being just that. What's Happening The system has slowed to a crawl whenever it touches the disk. Things appear to work at normal speed when dealing with memory. For example, typing this is fine, but saving it to disk from notepad gave me a 5-7 second pause when clicking save. The disks appear to be at 100% all the time (e.g. the light on the disk access on the PC is solidly on -- not even any flashing) In ProcExp it appears that the disk is barely being utilized at all: Intel RST reports that everything is fine: Other Details Prior to this happening, RST had reported that my drives were failing (one went bad, one was throwing SMART events). This made sense; they were at the tail end of their warranty and the PC is on almost all the time. I RMA'd the drives via Seagate. In the meantime, I'd purchased a 2TB drive because I didn't realize that the 1TB drives were under warranty. I figured I'd replace the other 1 TB drive with another 2 TB when it died but then discovered the warranty. AFAIK, I haven't done any major updates since 8.1 and it worked fine after those. Question(s) How can I troubleshoot this? What is the best way to try to figure out why disks are being maxed out despite the OS reporting barely any disk usage and that everything is OK? Given the failures, etc. that I describe above, is it possible that the problem could be the I/O on the motherboard itself? If so, how would I even be able to diagnose it? I'm betting the drives that Seagate gave me are refurbished (didn't think to look; that's dumb). Is it possible that the same model drive, refurbished, could somehow cause this? In terms of how RAID1 works, is it possible that one drive is "falling behind" somehow, and that the RAID1 is constantly trying to fix the mirroring? If so, this seems like Intel RST would report on it, but I wanted to consider it as an option.

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• WinXP - Having trouble sharing internet with 3G USB modem via ICS

  - by Carlos Nunez

  all! I've been banging my head against a wall with this issue for a few days now and am hoping someone can help out. I recently signed up for T-Mobile's webConnect 3G/4G service to replace the faltering (and slow) DSL connection in my apartment. The goal was to put the SIM in one of my old phones and use its built-in WLAN tethering feature to share Internet out to rest of my computers. I quickly found out that webConnect-provisioned SIMs do not work with regular smartphones, so I was forced to either buy a 4G-compatible router or tether one of my old laptops to my wireless router and share out that way. I chose the latter, and it's sharpening my inner masochistic self by the day. Here's the setup: GSM USB modem (via hub), ICS host - 10/100 Mbps Ethernet NIC, ICS "guest" - WAN port of my SMC WGBR14N wireless router in bridged mode (i.e. wireless access point). Ideally, this would make my laptop the DHCP server and internet gateway with the WAP giving everyone wireless coverage. I can browse internet on the host laptop fine. However, when clients try to connect, they get a DHCP-assigned IP from the laptop and are able to use the Internet for a few minutes before completely dying. After that happens, they are able to re-associate with the WAP and get IP addresses, but are unable to use Internet or resolve IP addresses until the laptop and router are restarted. If they do get access, it's very, very slow. After running Wireshark on the host machine, it turns out that this is because every TCP connection keeps getting RST. DNS seems to work. I would normally think the firewall is the culprit here, but when it drops packets, it drops them completely. The fact that TCP connections are being ACK'ed by the destination rules that out. Of course, none of the event Log isn't saying anything about what's going on. I also tried disabling power management on the NIC, since that's caused problems in the past; that didn't help either. I finally disabled receive-side scaling as per a Microsoft KB (that applied to Windows Server 2003, SP2) to no avail. I'm thinking of trying it with a different NIC (will be tough; don't have a spare Ethernet NIC around for the laptop), but I'm getting the impression that this simply doesn't work. Can anyone please advise? I apologise for the length of this post; all contributions are much appreciated! -Carlos.

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• Safer RAID5 rebuilds using partially failed disks?

  - by arcticmac

  There have been lots of articles posted recently about how RAID5 is dangerous because of long resilver times, and in particular because of increasing chances of encountering a URE during the resilver. Obviously this is a significant concern. However, it seems that in many cases of interest (as long as you're keeping some kind of eye on your disks), when it comes time to rebuild the array, the disk that I'm replacing is still mostly readable. If you try to explain this predicament to the average layperson, they are typically very confused as to why you have two almost completely functional disks but can't produce one working array. It seems to me that there ought to be some way to take advantage of this to make rebuilds safer, as long as I'm willing to have the RAID5 be read-only for a couple of days while it rebuilds. Conceptually, what I have in mind looks something like this: When a disk fails, immediately take the RAID5 offline or mount it read-only Attach a new disk (either in a spare bay, or externally via eSATA) and begin rebuilding it to replace the failed one. If known, perhaps start with the stripes in which the failure occurred, to minimize the chances of losing those if another disk fails. In the event that a second disk experiences a URE or other failure during the rebuild, try to source that data from the disk that is being replaced. Presumably if this happens, more rebuilding would be necessary. When complete, shut down the server, swap the replacement drive into the original bay if desired, and bring the array back up. Obviously such a process would not be appropriate for applications where uptime is critical or data loss cannot be tolerated, but it seems to me that this could help considerably to improve the reliability of RAID5. I assume that there's not a good way to implement a recovery like this at present, given that I haven't seen any indication of tools that are designed to do this, and that it seems like it would be rather obtuse to work out manually. Are there also technical issues with it that I haven't thought of (I'm still fairly new to RAID stuff)? Any thoughts on how hard something like this would be to implement (e.g. in linux md raid)?

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• Areca 1280ml RAID6 volume set failed

  - by Richard

  Today we hit some kind of worst case scenario and are open to any kind of good ideas. Here is our problem: We are using several dedicated storage servers to host our virtual machines. Before I continue, here are the specs: Dedicated Server Machine Areca 1280ml RAID controller, Firmware 1.49 12x Samsung 1TB HDDs We configured one RAID6-set with 10 discs that contains one logical volume. We have two hot spares in the system. Today one HDD failed. This happens from time to time, so we replaced it. Upon rebuilding a second disc failed. Normally this is no fun. We stopped heavy IO-operations to ensure a stable RAID rebuild. Sadly the hot-spare disc failed while rebuilding and the whole thing stopped. Now we have the following situation: The controller says that the raid set is rebuilding The controller says that the volume failed It is a RAID 6 system and two discs failed, so the data has to be intact, but we cannot bring the volume online again to access the data. While searching we found the following leads. I don't know whether they are good or bad: Mirroring all the discs to a second set of drives. So we would have the possibility to try different things without loosing more than we already have. Trying to rebuild the array in R-Studio. But we have no real experience with the software. Pulling all drives, rebooting the system, changing into the areca controller bios, reinserting the HDDs one-by-one. Some people are saying that the brought the system online by this. Some are saying that the effect is zero. Some say, that they blew the whole thing. Using undocumented areca commands like "rescue" or "LeVel2ReScUe". Contacting a computer forensics service. But whoa... primary estimates by phone exceeded 20.000€. That's why we would kindly ask for help. Maybe we are missing the obvious? And yes of course, we have backups. But some systems lost one week of data, thats why we'd like to get the system up and running again. Any help, suggestions and questions are more than welcome.

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• Setting up a WPA-PSK network card to connect to a WPA2 network

  - by mattshepherd

  I'm currently doing a spare-parts build to put a media computer in the living room, and having a devil of a time getting my Rosewill RNX-6300 wireless card to connect to my network. I'm trying to set it up using Windows as opposed to the proprietary Rosewill software -- the Rosewill software is a little over my head. It can find the network fine, but when I try to connect, I don't get the password prompt -- it moves straight to "validating identity," scans, and then says "Windows was not able to find a certificate to log you on to the wireless network Foo." The maddening thing is that the card was working fine a week ago, in the same box, using the same OS. I pulled everything out, swapped out the motherboard, and reinstalled Windows on a freshly wiped hard drive, and now I can't get it up and running again. Suggestions? I've taken several runs at it, including attempting to manually change the settings for the network to include WPA-PSK and AES and the password, and I'm a bit worried that I've totally boned everything. My router settings: ipconfig/all results from the XP box: Again, this card was working on this network a week ago. I can't figure out why I can't get it up and running now. There's no WPA2 on the card, just WPA and WPA-PSK: WPA-PSK was the only setting that would let me enter a network key. I had TKIP and AES as options there, but cipher type is AES on the router, so I chose that. (I tried TKIP later, when this didn't work, with the same results as described below.) So I set it to WPA-PSK / AES and entered my security key. It's mixed letters and numbers, 32 characters long. No joy. Still "waiting for reply" in the main screen, and "cannot find certificate" on the pop-up. And if I try again and return to the settings again, it is reset to Open/AES. It also re-enables 802.1x in the Authentication tab if I've deselected it with WPA-PSK. It also reshortens the password. I have no idea how I blundered into getting this working in the past. I am, as you can tell, far from proficient at this. It was working before, though. What am I getting wrong?

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• DVD ROM is not working

  - by Cyril N.

  (note: I don't know in which StackExchange site to put this question, I'll thank the moderator that will move it to a more appropriate place, if there is a S.E. available for my question). I have a DVD RW drive that is well listed in the bios, and if no CD is in, it is also present in the "My Computer" of my Fedora 16. But when I put a disc on it, the icon disapear from "My Computer", and I can not do anything with this ! (Like erasing a RW disc). I'd like to boot a Fedora 17 Live CD image. I burned it on an other computer but when I try to run it in bios, nothing is done and I'm redirected to Grub of my HD. The command cdrecord -scanbus shows this : wodim: Warning: controller returns wrong size for CD capabilities page. wodim: Cannot get CD capabilities data. 6,1,0 601) 'HD-DT%ST' 'DVD%RAM G@22NP20' '1&04' Removable CD-ROM And when I try to mount manually the disc, I got this error : mount: block device /dev/sr0 is write-protected, mounting read-only mount: /dev/sr0: can't read superblock Here's a paste of dmesg | grep sr0 : [ 5.161265] sr0: scsi-1 drive [ 5.161621] sr 6:0:1:0: Attached scsi CD-ROM sr0 [ 834.545978] sr0: Hmm, seems the drive doesn't support multisession CD's [ 841.731194] sr0: CDROM (ioctl) error, command: Get configuration 46 00 00 00 00 00 00 00 20 00 [ 842.021640] sr 6:0:1:0: [sr0] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE [ 842.021652] sr 6:0:1:0: [sr0] Sense Key : Aborted Command [current] [ 842.021662] sr 6:0:1:0: [sr0] Add. Sense: No additional sense information [ 842.021672] sr 6:0:1:0: [sr0] CDB: Read(10): 28 00 00 00 00 00 00 00 02 00 [ 842.021688] end_request: I/O error, dev sr0, sector 0 [ 842.021697] Buffer I/O error on device sr0, logical block 0 [ 842.023715] sr 6:0:1:0: [sr0] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE [ 843.048203] sr 6:0:1:0: [sr0] Sense Key : Aborted Command [current] [ 843.048211] sr 6:0:1:0: [sr0] Add. Sense: No additional sense information [ 843.048219] sr 6:0:1:0: [sr0] CDB: Read(10): 28 00 00 00 00 00 00 00 01 00 [ 843.048234] end_request: I/O error, dev sr0, sector 0 [ 843.048274] EXT4-fs (sr0): unable to read superblock [ 843.063155] sr0: CDROM (ioctl) error, command: Get configuration 46 00 00 00 00 00 00 00 20 00 [ 843.075904] sr0: CDROM (ioctl) error, command: Get configuration 46 00 00 00 00 00 00 00 20 00 [ 843.220512] sr 6:0:1:0: [sr0] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE [ 843.220522] sr 6:0:1:0: [sr0] Sense Key : Aborted Command [current] [ 843.220530] sr 6:0:1:0: [sr0] Add. Sense: No additional sense information [ 843.220538] sr 6:0:1:0: [sr0] CDB: Read(10): 28 00 00 00 00 00 00 00 01 00 [ 843.220553] end_request: I/O error, dev sr0, sector 0 [ 843.220609] FAT-fs (sr0): unable to read boot sector The lines from Sense Key .. (line 6) to DRIVER_SENSE (line 11) are repeating a lot. I then changed my DVD player with an other spare one I had, and the disc didn't boot neither. I then changed the IDE cable, but still no success. What can I do to make it work? Thanks for your help.

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• How should I convert a physical drive to a VHD for use with VirtualPC?

  - by RBerteig

  I have the hard disks from a PC that was happily running Windows Me until is it suffered an unknown hardware failure. The drives are intact, and can be mounted and read on other PCs. We have data backups, but there is licensed software installed that may not be possible to migrate to newer versions running on a more modern platform making the idea of just booting a virtual image attractive. Is it possible to make VHDs from the drives such that I can boot them in VirtualPC? If not VirtualPC, would it be possible in any other virtualization tool? Edit: Some more details.... The system was running Windows Me, but upgraded from Windows 95 (or possibly 98). It can't have been more than a Pentium II, but I will have to look at the motherboard to confirm that. There were no "exotic" devices installed, and nothing beyond the usual legacy stuff that would need to survive into a virtual machine. The licensed software did not have a dongle, so I won't need to worry about virtualizing a physical dongle of some kind. Licenses were probably died to the disk serial number. There were two HDs, both IDE. The boot disk is about 6GB, and the spare data disk is 12GB, but nearly empty. I have a small bias in favor of VirtualPC just because its free and I've used it successfully in the past. But this is a good excuse to revisit the state of the art. I do know from direct experience that it is possible to install and boot DOS 5.0 and Win95 in VirtualPC, but the VM extensions weren't available so the experience isn't as seamless as I would have liked. A very old DirectX game that failed miserably under XP SP2 runs really nicely on that VM, and actually plays better in a lot of ways than it did on period hardware, so that gives me hope that this is possible. Edit 2: Well, I'm closer than I was when I asked... so thanks to all for helpful suggestions and hints to what I should be trying. I used WinImage to copy the disks, and VirtualPC 2007 to attempt to boot. So far, I have it booting in safe mode, but hanging with a black screen otherwise. I strongly suspect that the copy of Artisoft Lantastic 8.0 (anyone else remember them?) that is still installed for networking with even older PCs that mostly don't exist any more is the culprit there. In my infinite free time, I will try to resolve the differences between a Safe Mode boot and a normal boot, and feel that it is likely to yield to pressure. I'd accept more than one answer if I could... this isn't as black and white a question as the one accepted answer convention assumes.

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• Hot-swap drive got new name, can I change it on-the-fly?

  - by T.J. Crowder

  One of the HDDs in my server's RAID config failed, so I took it out of the array and had the data center hot-swap it. They've done that, but now the new drive is /dev/sdc rather than /dev/sda. I suspect — correct me if I'm wrong — that if I reboot the server, it will be /dev/sda again, so I'm hesitant to add it back to the array as /dev/sdc because I don't want to lay a trap for myself to fall into on the next reboot. I'd just as soon not reboot the server if I don't need to (if I do need to, well, too bad for me). Is there a way I can change the device name from /dev/sdc to /dev/sda without rebooting? This is on Ubuntu 10.04 LTS. It's an md array ("Linux Software RAID"), where currently one of the devices (there are a couple of them) looks like this ("degraded" because I've removed the old /dev/sda from it): # mdadm --detail /dev/md0 /dev/md0: Version : 00.90.03 Creation Time : Sun Oct 11 21:07:54 2009 Raid Level : raid1 Array Size : 97536 (95.27 MiB 99.88 MB) Used Dev Size : 97536 (95.27 MiB 99.88 MB) Raid Devices : 2 Total Devices : 1 Preferred Minor : 0 Persistence : Superblock is persistent Update Time : Thu Jun 30 09:31:16 2011 State : clean, degraded Active Devices : 1 Working Devices : 1 Failed Devices : 0 Spare Devices : 0 UUID : 496be7a5:ab9177ed:7792c71e:7dc17aa4 Events : 0.112 Number Major Minor RaidDevice State 0 8 17 0 active sync /dev/sdb1 1 0 0 1 removed Thanks, Update: Reading through the kernel md documentation, I suspect that if the name changes on reboot, it won't matter. (Good design, that.) Here's why: Boot time autodetection of RAID arrays When md is compiled into the kernel (not as module), partitions of type 0xfd are scanned and automatically assembled into RAID arrays. This autodetection may be suppressed with the kernel parameter "raid=noautodetect". As of kernel 2.6.9, only drives with a type 0 superblock can be autodetected and run at boot time. The kernel parameter "raid=partitionable" (or "raid=part") means that all auto-detected arrays are assembled as partitionable. I do have md compiled into the kernel, so I'm rebuilding the array now and will do the reboot to see what happens. Even if it works, the above doesn't answer the question I actually asked, so unless someone comes along and answers that question in the meantime (I'd be interested, even if it's not necessary for what I'm doing this very moment), I'll just delete the question to keep noise down.

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• Cannot install grub to RAID1 (md0)

  - by Andrew Answer

  I have a RAID1 array on my Ubuntu 12.04 LTS and my /sda HDD has been replaced several days ago. I use this commands to replace: # go to superuser sudo bash # see RAID state mdadm -Q -D /dev/md0 # State should be "clean, degraded" # remove broken disk from RAID mdadm /dev/md0 --fail /dev/sda1 mdadm /dev/md0 --remove /dev/sda1 # see partitions fdisk -l # shutdown computer shutdown now # physically replace old disk by new # start system again # see partitions fdisk -l # copy partitions from sdb to sda sfdisk -d /dev/sdb | sfdisk /dev/sda # recreate id for sda sfdisk --change-id /dev/sda 1 fd # add sda1 to RAID mdadm /dev/md0 --add /dev/sda1 # see RAID state mdadm -Q -D /dev/md0 # State should be "clean, degraded, recovering" # to see status you can use cat /proc/mdstat This is the my mdadm output after sync: /dev/md0: Version : 0.90 Creation Time : Wed Feb 17 16:18:25 2010 Raid Level : raid1 Array Size : 470455360 (448.66 GiB 481.75 GB) Used Dev Size : 470455360 (448.66 GiB 481.75 GB) Raid Devices : 2 Total Devices : 2 Preferred Minor : 0 Persistence : Superblock is persistent Update Time : Thu Nov 1 15:19:31 2012 State : clean Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0 UUID : 92e6ff4e:ed3ab4bf:fee5eb6c:d9b9cb11 Events : 0.11049560 Number Major Minor RaidDevice State 0 8 1 0 active sync /dev/sda1 1 8 17 1 active sync /dev/sdb1 After bebuilding completion "fdisk -l" says what I have not valid partition table /dev/md0. This is my fdisk -l output: Disk /dev/sda: 500.1 GB, 500107862016 bytes 255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00057d19 Device Boot Start End Blocks Id System /dev/sda1 * 63 940910984 470455461 fd Linux raid autodetect /dev/sda2 940910985 976768064 17928540 5 Extended /dev/sda5 940911048 976768064 17928508+ 82 Linux swap / Solaris Disk /dev/sdb: 500.1 GB, 500107862016 bytes 255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x000667ca Device Boot Start End Blocks Id System /dev/sdb1 * 63 940910984 470455461 fd Linux raid autodetect /dev/sdb2 940910985 976768064 17928540 5 Extended /dev/sdb5 940911048 976768064 17928508+ 82 Linux swap / Solaris Disk /dev/md0: 481.7 GB, 481746288640 bytes 2 heads, 4 sectors/track, 117613840 cylinders, total 940910720 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x00000000 Disk /dev/md0 doesn't contain a valid partition table This is my grub install output: root@answe:~# grub-install /dev/sda /usr/sbin/grub-setup: warn: Attempting to install GRUB to a disk with multiple partition labels or both partition label and filesystem. This is not supported yet.. /usr/sbin/grub-setup: error: embedding is not possible, but this is required for cross-disk install. root@answe:~# grub-install /dev/sdb Installation finished. No error reported. So 1) "update-grub" find only /sda and /sdb Linux, not /md0 2) "dpkg-reconfigure grub-pc" says "GRUB failed to install the following devices /dev/md0" I cannot load my system except from /sdb1 and /sda1, but in DEGRADED mode... Anybody can resolve this issue? I have big headache with this.

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• PSU failing or Mainboard failing?

  - by Andrei Rinea

  I am having some troubles lately powering on my desktop workstation. While starting up the PC after being off for hours (usually at least 8 hours) it randomly fails to do so. What happens is that : I press the power button; nothing happens I can hear a moderate buzzing noise at the back of the PC (near the PSU); but I can't say for sure that it's not from the mainboard. If I insist pressing the power button a few times in 1-2 minutes it'll start Another route would be that instead of (3) I will plug off the power cable from the PSU and wait for 30 seconds. Then I will press the power on and keep it for 30-60 seconds (I had some success at notebooks with a similar approach). Then I will plug back the cable in the PSU, press only once the power button and it will start normally. Also while running normally I keep hearing some low buzzing which seems to be fan-RPM-related (i.e. when processing images or doing CPU intensive work). What should I look into? UPDATE It's getting worse. It took more than 10 retries today and almost 20 minutes to start the computer. I tried the paperclip trick and the PSU behaves perfectly. I managed to start the computer like so : I pressed the on-button a few times and then left the PC in a pre-startup state (the fans were working the buzzing noise was strong and I went to eat. I thought I won't lit the house on fire so fast and without smelling. Back, after 10-15 min the computer booted up! Discussed with a fellow at Intel and he told me the capacitors on the mainboard are probably a bit shot. If they are shot, he said, it should start up warm perfectly. So I did restart it, warm, a few times (5 sec cooldown and then 40 sec cooldown and it started up perfectly). I can either replace the capacitors on the mainboard (doesn't sound worth it or replace the mainboard (this one sucks too :)) ) FINAL INFO : It was the PSU after all. Although it was powering the IDEs and SATAs the Mainboard power module was failing. I bought another mainboard just to find out that this wasn't the cause. Now I'll have to return it somehow. The spare PSU is now in the computer and doing well.. Although larger (500W), it's like a plane taking off.. I need a better one.

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