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• SQL Server Backup File Significantly Smaller After Table Recreation

  - by userx

  We run automated weekly backups of our SQL Server. The database in question is configured for Simple Recovery. We backup using Full, not differential. Recently, we had to re-create one of our tables with data in it (making 2 varchar fields a couple characters longer). This required running a script which created a new table, copied the data over, and then dropped the old. This worked correctly. Oddly though, our weekly backup files now SHRANK by over 75%! The tables don't have large indexes. All data was copied over correctly (and verified). I've verified that we are doing full and not incremental backups. The new files restore just fine. I can't seem to figure out why the backup files would have shrank so much? I've also noticed that they get about 10 MB larger every week, even though less than that amount of data is being added. I'm guessing that I'm simply not understanding something. Any insight would be appreciated.

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• Slow network file transfer (under 20KB/s) on newly built x64 Win7

  - by Mangoshake

  I am getting <20KB/s for local network file transfer. If I transfer a very small file (less than 100KB) it would start quickly then slow down to <20KB/s. all subsequently network file transfer would be slow, a reboot is needed to reset this. If I transfer a large file it would be stuck on calculating for a long time and then begin with <20KB/s immediately. This is a newly built desktop running Windows 7 x64 SP1. Realtek gigabit LAN from the motherboard (ASRock Extreme3 gen3). Problematic speed is observed on the private LAN, both through ethernet and WiFi. The Router is D-Link DIR-655. Remote Differential Compression is off. Drivers are up-to-date from ASRock's website. I have tested network file transfer to and from another Windows 7 laptop and a MacBook Pro, so I am fairly certain it is the desktop's problem. The slow speed only happens with one direction also, outbound from the desktop, regardless of whether I initiate the file transfer action from the origin or the destination. Inbound network file transfer and internet speeds are fine, so I don't think this is a hardware issue. I am getting 74.8MB/s internet upload speed from speedtest.net (http://www.speedtest.net/result/1852752479.png). Inbound network file transfer I can get around 10-15MB/s. I am hoping this community has some insight for me to troubleshoot this. I don't see anything obviously related from the Event Viewer, and beyond that I just don't know where else to look. Any suggestions are greatly appreciated, thank you in advance.

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• Which is the fastest way to move 1Petabyte from one storage to a new one?

  - by marc.riera

  First of all, thanks for reading, and sorry for asking something related to my job. I understand that this is something that I should solve by myself but as you will see its something a bit difficult. A small description: Now Storage = 1PB using DDN S2A9900 storage for the OSTs, 4 OSS , 10 GigE network. (lustre 1.6) 100 compute nodes with 2x Infiniband 1 infiniband switch with 36 ports After Storage = Previous storage + another 1PB using DDN S2A 990 or LSI E5400 (still to decide) (lustre 2.0) 8 OSS , 10GigE network 100 compute nodes with 2x Infiniband Previous experience: transfered 120 TB in less than 3 days using following command: tar -C /old --record-size 2048 -b 2048 -cf - dir | tar -C /new --record-size 2048 -b 2048 -xvf - 2>&1 | tee /tmp/dir.log So , big problem here, using big mathematical equations I conclude that we are going to need 1 month to transfer the data from one side to the new one. During this time the researchers will need to step back, and I'm personally not happy with this. I'm telling you that we have infiniband connections because I think that may be there is a chance to use it to transfer the data using 18 compute nodes (18 * 2 IB = 36 ports) to transfer the data from one storage to the other. I'm trying to figure out if the IB switch will handle all the traffic but in case it just burn up will go faster than using 10GigE. Also, having lustre 1.6 and 2.0 agents on same server works quite well, with this there is no need to go by 1.8 to upgrade the metadata servers with two steps. Any ideas? Many thanks Note 1: Zoredache, we can divide it in two blocks (A)600Tb and (B)400Tb. The idea is to move (A) to new storage which is lustre2.0 formated, then format where (A) was with lustre2.0 and move (B) to this lustre2.0 block and extend with the space where (B) was. This way we will end with (A) and (B) on separate filesystems, with 1PB each.

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• Tidy up old Windows Server Backup snapshots

  - by dty

  Hi, I'm running wbadmin from a scheduled job, backing up my C: and D: drives to my E: and (I believe!) including the system state: wbadmin start backup -backuptarget:e: -include:c:,d: -allCritical -noVerify -quiet I'd like to delete old backups, but I'm concerned that all the information I can find says to use wbadmin to delete old system state backups, and vssadmin to delete other backups. As far as I know, my backups ARE system state backups, but are using VSS on E: for storage, so I'm worried about trying either of these techniques for fear of losing all my backups. This is a home network, so I don't have a spare server to test this on. I'm also happy to simply restrict the space used on E:, but I can't make sense of the difference between the /for and /on parameters of the relevant vssadmin command. For reference, here's the output of vssadmin show shadows: Contents of shadow copy set ID: {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx} Contained 1 shadow copies at creation time: 07/01/2011 08:12:05 Shadow Copy ID: {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx} Original Volume: (E:)\\?\Volume{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}\ Shadow Copy Volume: \\?\GLOBALROOT\Device\HarddiskVolumeShadowCopy83 Originating Machine: x.y.com Service Machine: x.y.com Provider: 'Microsoft Software Shadow Copy provider 1.0' Type: DataVolumeRollback Attributes: Persistent, No auto release, No writers, Differential [... repeated a lot...] vssadmin show shadowstorage: Shadow Copy Storage association For volume: (C:)\\?\Volume{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}\ Shadow Copy Storage volume: (C:)\\?\Volume{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}\ Used Shadow Copy Storage space: 0 B Allocated Shadow Copy Storage space: 0 B Maximum Shadow Copy Storage space: 5.859 GB Shadow Copy Storage association For volume: (D:)\\?\Volume{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}\ Shadow Copy Storage volume: (D:)\\?\Volume{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}\ Used Shadow Copy Storage space: 0 B Allocated Shadow Copy Storage space: 0 B Maximum Shadow Copy Storage space: 40.317 GB Shadow Copy Storage association For volume: (E:)\\?\Volume{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}\ Shadow Copy Storage volume: (E:)\\?\Volume{xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}\ Used Shadow Copy Storage space: 168.284 GB Allocated Shadow Copy Storage space: 171.15 GB Maximum Shadow Copy Storage space: UNBOUNDED wbadmin get versions: Backup time: 07/01/2011 03:00 Backup target: 1394/USB Disk labeled xxxxxxxxx(E:) Version identifier: 01/07/2011-03:00 Can Recover: Volume(s), File(s), Application(s), Bare Metal Recovery, System State [... repeated a lot...]

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• Slow Local Network, Windows 7, Snow Leopard, WiFi/Wired

  - by WerkkreW

  Hello - I am experiencing really poor local network performance in my home. I was recently using a Linksys WRT54G Router with DD-WRT on it, and a couple comparable Linksys-G PCI cards for connectivity but decided to upgrade hoping it would help with my performance issues. The computers in my house are connected as follows: Comcast Business Class Commercial 25mbps/10mbps (Verified with SpeakEasy and Speedtest.net) D-Link DGL-4500 Wireless N Router Windows 7x64 - D-Link DWA-552 Wireless-N Windows 7x64 - D-Link DWA-552 Wireless-N Mac Mini 10.6.2 - AirPort Extreme N Playstation 3, Hard Wired Xbox 360, Hard Wired Essentially the problem is very specific. Web browsing and uploading/downloading files from the internet is fine, more than fine. But if I want to say, Stream a video from one of my Windows 7 computers to my PS3, or copy a large video file between either of the PC's or the Mac, I get a consistent 500-900Kbps throughput at the high end. If I open my network browser, or try to browse my homegroup the response time is horrible. Both of my Windows computers are showing Strong wireless signals with a connection speed of 300Mbps. I know I can never expect to achieve anything near those speeds, but 500Kbps? Here is what I have tried so far: Enabled Single mode N-only and N/G Only on router WPA2 with AES Encrpytion Disabled "Remote Differential Compression" in Windows 7 Disabled TCP "Auto-Tuning" Used other software for file copies such as "Teracopy" I am at the end of my rope. Unfortunately I live in a 75 year old home with plaster walls, so hard-wiring my entire house isn't really an option I can handle right now. Any ideas to help me get decent speed when transferring files across my network would be greatly appreciated.

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• Does the OSS Backup Solution amanda.org support sparse files?

  - by user97961

  I want to (or better have to) do Backups of my KVM Virtual Machine images. I have searched for days for a good Backup Soloution. I know amanda is a very good solution. It would be kinf if someone kenn tell me if the following is supported: Trigger the Creation of LVM Snapshot (by invoking a Shell Script that I will write for that purpose) Do a Differential/Delta Backup on my KVM LVM qcow2 sparse file. = I only want to copy the actually changed bits/bytes (=Delta Backup). And it has to support that the file to be backuped up is a sparse file. (Rsync seems to have some kind of problems in regard to this (if the file does not exist yet on the other side... Then it will create a full file, not a sparse file)) Release the LVM Snapshot (By invoking a Script that I will write for that purpose) It's strange, I have nowhere found any documentation about this fact when searching the internet. Zmanda (Commercial Edition) has support vom XEN VM Backup (but not for KVM as far as I can tell)...

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• Backup Exec tape rotation guidelines

  - by HannesFostie

  Hi We use Backup Exec to take care of our backups for our data server, exchange server, and one more set of systems. Each of these 3 is being done on a separate "set" of tapes. Our goal is to be able to roll back a full 2 weeks, with 1 full backup each weekend and differential/incremental backups in between (the difference between the two in our case isn't very big, because the employees mostly use a very similar set of files throughout the week). While playing around with the settings on how to achieve this, we set the time for BE to keep the full backup to 14 days, but because we have too much data this would require manual intervention each time to erase a certain tape and use that. What I would like to know is what kind of guidelines, tricks, tips and general "stuff to think about" you keep in mind when designing your backup schedule. The type of backups (full/diff/incr) isn't of that much importance in our case as it's more or less set in stone. Made this community wiki as it's not a very specific question. Thanks in advance!

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• Network connection keeps dropping - bad hardware?

  - by Bill Sambrone

  Hello all, I've into a bit of a wall with a client of mine. In an office of 20 people, he is the only one who experiences broken connections to his mapped network drives. I have everyone set up with about 6 mapped drives, all pointing to the same server (no DFS), and everyone else can access them lightning fast. The environment consists of a mix of Windows 7 and XP machines, all 32-bit. The server holding the data everyone is mapping to is running on Server 2008 R2, and is a domain controller. We recently swapped out their old 10/100 switch for a shiny new Dell PowerConnect gigabit switch. We have also replaced an old dying Sonicwall with a shiny new one. Everything is running on an ESX host except for the DC, where everyone is getting data from. In my client's office, we have done the following: Swapped out his computer (Win7 and XP box) Swapped out the desktop switch in his office Removed the desktop switch in his office Changed out the network cable going to the wall Ran 'net config server /autodisconnect:-1' on the server Disabled remote differential compression on his current Win7 box When we swapped out his network cable, everything seemed fine for about 4 days. Normally I would get a phone call a couple times per day letting me know that Outlook has crashed (there is a 9GB PST living on the server he is always connected to), or that his software he is running from his L drive has crashed. I almost thought I had this solved, but after we rebooted the DC the other night he all of a sudden couldn't stay connected to his mapped network drives for more than 10 minutes. When I ran 'net use' from the command prompt, it listed all the network drives where were randomly in a state of 'OK', 'Disconnected', or 'Reconnecting'. What else should I try? Maybe there is bad wiring in the wall, patch panel, or a bad port in the new switch I have in the server room?

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• Slow Local Network, Windows 7, Snow Leopard, WiFi/Wired

  - by WerkkreW

  I am experiencing really poor local network performance in my home. I was recently using a Linksys WRT54G Router with DD-WRT on it, and a couple comparable Linksys-G PCI cards for connectivity but decided to upgrade hoping it would help with my performance issues. The computers in my house are connected as follows: Comcast Business Class Commercial 25mbps/10mbps (Verified) D-Link DGL-4500 Wireless N Router Windows 7x64 - D-Link DWA-552 Wireless-N Windows 7x64 - D-Link DWA-552 Wireless-N Mac Mini 10.6.2 - AirPort Extreme N Playstation 3, Hard Wired Xbox 360, Hard Wired Essentially the problem is very specific. Web browsing and uploading/downloading files from the internet is fine, more than fine. But if I want to say, Stream a video from one of my Windows 7 computers to my PS3, or copy a large video file between either of the PC's or the Mac, I get a consistent 500-900Kbps throughput at the high end. If I open my network browser, or try to browse my homegroup the response time is horrible. Both of my Windows computers are showing Strong wireless signals with a connection speed of 300Mbps. I know I can never expect to achieve anything near those speeds, but 500Kbps? Here is what I have tried so far: Enabled Single mode N-only and N/G Only on router WPA2 with AES Encrpytion Disabled "Remote Differential Compression" in Windows 7 Disabled TCP "Auto-Tuning" Used other software for file copies such as "Teracopy" I am at the end of my rope. Unfortunately I live in a 75 year old home with plaster walls, so hard-wiring my entire house isn't really an option I can handle right now. Any ideas to help me get decent speed when transferring files across my network would be greatly appreciated.

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• Converting PDF eBooks into a Kindle format

  - by Ender

  Over the past couple of years I've amassed quite a collection of guides, tutorials and ebooks in PDF format. A lot of these are quite useful for work, especially PDF documentation, and rather than have to be at a computer every time I want to read how to do something in Sitecore or to read through a software testing ebook I'd like to do it on my brand-spanking-new Kindle. However, even though there is now a native PDF reader on the Kindle due to the nature of PDF's they are practically unreadable. The text doesn't wrap due to how PDF's are sized and so far after a bunch of Google searches I've yet to find a viable solution to get my PDF's converted into a readable Kindle format. Sometimes these books have code or pictures/tables in them, but most of the time they're text-heavy and to be honest I'd be surprised if there wasn't a free tool to handle the converting of PDF to one of the (seemingly many) Kindle formats. So, can anyone help me out with this? EDIT: I've tried Calibre, and have checked their forums to play with some of the advanced settings, yet the solutions available seem to be extremely poor, especially if the book you're attempting to read contains equations, code, or anything outside of plain text. I've also tried Amazon's conversion service, which wasn't much help with such documents. The best way I have found so far is to build the entire thing over again in ePub or RTF format and convert to MOBI from there. This works for text-heavy books with tables, but anything technical still isn't covered. Can anyone help with this?

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• EC2 Auto-Scaling with Spot and On-Demand Instances?

  - by platforms

  I'm looking to optimize the cost of our auto-scaling EC2 groups by having them launch spot instances instead of on-demand instances. What I really want is to be able to keep some servers in the group as on-demand instances, regardless of what happens to the spot instance pricing market. Then I want any additional servers in the group, above my configured minimum, to be spot instances. I'm generally OK with the delay in adding servers via spot requests. I can't seem to find any way to do this and I've tried to scour the AWS documentation. It appears that an ASG can either be on-demand or spot, but not a hybrid. I could possibly manually add an on-demand instance to the Elastic Load Balancer assigned to the auto-scaling group, but then the load of that server would not be factored into the auto-scaling measurements and triggers. I suppose I could enter a ridiculously high bid price in order to ensure that I always get the servers I need, but then I look at the pricing history and see occasional large spikes. The AWS documentation is at odds with itself, since in one place it says that if you enter a server minimum, that number is "ensured" to be there. But then when you read about spot instances, there are no assurances. The price differential for spot is compelling, so I'd like to leverage that as much as I can while still maintaining an always-on baseline. Is this possible?

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• Server 2012 - transparent SMB failover without shared discs, possible?

  - by TomTom

  here is the scenario - there is a small set (200gb around) of data that I HAVE to keep available. Those are basically shared VHD images that serve as master images for a lot of our VM's - they then run in differential discs off those. The whole set is "mostly read only". In more detail: A file that IS there and IS used will NEVER change. I may delete files (when absolutely not in use) and add new files, but a file that is there once gets read protection set and that it is until it is retired. Obviously, I need as much uptime as possible. SO FAR we run that by having this directory local on every Hyper-V server. Now I think moving this into our storage fabric. Due to the "it HAS to be there" I pretty much want a share nothing architecture. DFS would be perfect for this - a file never changes, so replication would work nicely. Folders could be replicated to a number of servers, all would reference them from there. Now, that hyper-V supports SMB that could be a good idea to isolate these on a number of servers - we try to move into a scenario where the storage is more centralized. Server 2012 supports always on shares, but it seems that this only works with a clustered disc behind. Is there any way around this for read only file stores? All documentation points to stuff like a shared JBOD - but that would leave me open for file system corruption. I really plan to go quite separately here, vertically - 2 servers, both with SSD only for this, both with their own 2000W separate USV, both with enough bandwidth to handle everything thrown at them (note to everyone tinking this is 10G - this would be SLOW and EXPENSIVE compared to a nice Infiniband backbone). The real crux is that this is an edge case obviously - as the files are read only once in use.

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• Change the background color of selected text in Google Docs to increase readability [migrated]

  - by gene_wood

  How can I override or change the background color of text selected in Google Docs? It is difficult for me to see the difference and I would like to increase the contrast or difference. After Google restyled Google Docs last year (or earlier this year), I've been unable to see selected text. It's possible this is a visual deficiency with my eyes. In Google Docs, under both Google Chrome (17.0.963.83 (Official Build 127885) m) and Firefox (11.0), when I select text inside a Google Doc, the selected text has a background of color #d6e0f5. Compare this to the default browser background color of #2f65c0. (I determined the color of the selected text background by taking a screenshot and using the color picker tool in Photoshop). I've tested this using a brand new Firefox profile as well as google chrome profile. Here's a section of a screenshot showing the selected text : I've tried using a userscript to override the CSS to go back to the default text selection color using the "Stylish" plugin with this css : ::selection { background:#2f65c0; color:#ffffff; } ::-moz-selection { background:#2f65c0; color:#ffffff; } ::-webkit-selection { background:#2f65c0; color:#ffffff; } This code works on other sites, but I'm unable to get it to work on Google Docs. (I tested on other sites but applying the userscript to a different domain and using bright yellow instead of the default dark blue #2f65c0.) When you use Google Docs, do you have the same color background for selected text or something different? (To test this, browse to docs.google.com , create a document, type text into the document, select the text with the mouse by dragging over it, take a screenshot, load the screenshot up in an image editor and determine the background color of the selected text.) This color differential (between light blue #d6e0f5 and white #fffff) may be easy to see for others and the problem lies with my eyes.

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• Advice on cloning disk

  - by hks

  I'm going to buy a second disk for backup, the same size as my laptops. I want to mount it in a casing via usb and backup an entire hdd every soemtime. That's because I want the posibility to just switch drives in case of something goes wrong. I'm using Linux and obviously the right tool seems to be dd. The thing is that my laptop drive has a speed of around 50-70 MB/s and usb 2.0 is 57 MB/s. So to copy my 250GB disk should take me more than 1 hour if I'm lucky. I can't wait this much. I want some differential backup. I read one of JWZ articles. In it he gives more details for using rsync on Mac. He writes that there is possibility of making rsync'ed disk bootable. So my question is: how to make rsync'ed hdd bootable under Linux or are there other 'quick backup' tools for Linux that would allow me to just swap drives? Or should I just stick to dd :( ?

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• How to ensure local file is up-to-date or ahead (dropbox sync) before truecrypt auto-mount it?

  - by user620965

  There are a lot tutorials out there that states that dropbox build-in encryption is not secure enought. That tutorials recommands to sync a truecrypt container file to have all files in it securely encrypted. This setup is know to be limited. You can NOT have that truecrypt container file mounted on the same time on more than one location - if you have inserted changes to the contents of the container in more then one location at a time then this setup produces a conflict on the container file in the dropbox system - resulting in one container file for each location. In my case that issue is not relevant - i do not use my data on more than one location at a time. I want to use the auto-mount feature of truecrypt on startup of windows 7 to have a zero configuration environment - and start working right away. But i want to ensure that the local truecrypt container file is up-to-date before truecrypt mounts it automatically - imagine you updated the contents of the container on your primary location and your secondary location was off for a long time. In that case it can take "a long time" till dropbox sync is complete (e.g. depending on your internet connection and the size of the container file). There is a option in truecrypt that ensures that truecrypt do not update the timestamp of the container file - which speeds up the sync, because dropbox client is doing a differential sync then instead of a time consuming full-sync. That is an improvement to that setup, but this do not fix my issue. The question is how to make the auto-mount function wait for the container file to be up-to-date (updated by dropbox)? In contrast: if the file was changed local, but remote file (in the dropbox cloud system) is still old (not jet updated by the sync process / or process is progress), should not make truecrypt to wait for the sync. Suggestions?

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• SQL SERVER – Sends backups to a Network Folder, FTP Server, Dropbox, Google Drive or Amazon S3

  - by pinaldave

  Let me tell you about one of the most useful SQL tools that every DBA should use – it is SQLBackupAndFTP. I have been using this tool since 2009 – and it is the first program I install on a SQL server. Download a free version, 1 minute configuration and your daily backups are safe in the cloud. In summary, SQLBackupAndFTP Creates SQL Server database and file backups on schedule Compresses and encrypts the backups Sends backups to a network folder, FTP Server, Dropbox, Google Drive or Amazon S3 Sends email notifications of job’s success or failure SQLBackupAndFTP comes in Free and Paid versions (starting from $29) – see version comparison. Free version is fully functional for unlimited ad hoc backups or for scheduled backups of up to two databases – it will be sufficient for many small customers. What has impressed me from the beginning – is that I understood how it works and was able to configure the job from a single form (see Image 1 – Main form above) Connect to you SQL server and select databases to be backed up Click “Add backup destination” to configure where backups should go to (network, FTP Server, Dropbox, Google Drive or Amazon S3) Enter your email to receive email confirmations Set the time to start daily full backups (or go to Settings if you need Differential or  Transaction Log backups on a flexible schedule) Press “Run Now” button to test You can get to this form if you click “Settings” buttons in the “Schedule section”. Select what types of backups and how often you want to run them and you will see the scheduled backups in the “Estimated backup plan” list A detailed tutorial is available on the developer’s website. Along with SQLBackupAndFTP setup gives you the option to install “One-Click SQL Restore” (you can install it stand-alone too) – a basic tool for restoring just Full backups. However basic, you can drag-and-drop on it the zip file created by SQLBackupAndFTP, it unzips the BAK file if necessary, connects to the SQL server on the start, selects the right database, it is smart enough to restart the server to drop open connections if necessary – very handy for developers who need to restore databases often. You may ask why is this tool is better than maintenance tasks available in SQL Server? While maintenance tasks are easy to set up, SQLBackupAndFTP is still way easier and integrates solution for compression, encryption, FTP, cloud storage and email which make it superior to maintenance tasks in every aspect. On a flip side SQLBackupAndFTP is not the fanciest tool to manage backups or check their health. It only works reliably on local SQL Server instances. In other words it has to be installed on the SQL server itself. For remote servers it uses scripting which is less reliable. This limitations is actually inherent in SQL server itself as BACKUP DATABASE command  creates backup not on the client, but on the server itself. This tool is compatible with almost all the known SQL Server versions. It works with SQL Server 2008 (all versions) and many of the previous versions. It is especially useful for SQL Server Express 2005 and SQL Server Express 2008, as they lack built in tools for backup. I strongly recommend this tool to all the DBAs. They must absolutely try it as it is free and does exactly what it promises. You can download your free copy of the tool from here. Please share your experience about using this tool. I am eager to receive your feedback regarding this article. Reference: Pinal Dave (http://blog.SQLAuthority.com)   Filed under: PostADay, SQL, SQL Authority, SQL Backup and Restore, SQL Query, SQL Server, SQL Tips and Tricks, SQL Utility, SQLServer, T SQL, Technology

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• Problems implementing a screen space shadow ray tracing shader

  - by Grieverheart

  Here I previously asked for the possibility of ray tracing shadows in screen space in a deferred shader. Several problems were pointed out. One of the most important problem is that only visible objects can cast shadows and objects between the camera and the shadow caster can interfere. Still I thought it'd be a fun experiment. The idea is to calculate the view coordinates of pixels and cast a ray to the light. The ray is then traced pixel by pixel to the light and its depth is compared with the depth at the pixel. If a pixel is in front of the ray, a shadow is casted at the original pixel. At first I thought that I could use the DDA algorithm in 2D to calculate the distance 't' (in p = o + t d, where o origin, d direction) to the next pixel and use it in the 3D ray equation to find the ray's z coordinate at that pixel's position. For the 2D ray, I would use the projected and biased 3D ray direction and origin. The idea was that 't' would be the same in both 2D and 3D equations. Unfortunately, this is not the case since the projection matrix is 4D. Thus, some tweak needs to be done to make this work this way. I would like to ask if someone knows of a way to do what I described above, i.e. from a 2D ray in texture coordinate space to get the 3D ray in screen space. I did implement a simple version of the idea which you can see in the following video: video here Shadows may seem a bit pixelated, but that's mostly because of the size of the step in 't' I chose. And here is the shader: #version 330 core uniform sampler2D DepthMap; uniform vec2 projAB; uniform mat4 projectionMatrix; const vec3 light_p = vec3(-30.0, 30.0, -10.0); noperspective in vec2 pass_TexCoord; smooth in vec3 viewRay; layout(location = 0) out float out_AO; vec3 CalcPosition(void){ float depth = texture(DepthMap, pass_TexCoord).r; float linearDepth = projAB.y / (depth - projAB.x); vec3 ray = normalize(viewRay); ray = ray / ray.z; return linearDepth * ray; } void main(void){ vec3 origin = CalcPosition(); if(origin.z < -60) discard; vec2 pixOrigin = pass_TexCoord; //tex coords vec3 dir = normalize(light_p - origin); vec2 texel_size = vec2(1.0 / 600.0); float t = 0.1; ivec2 pixIndex = ivec2(pixOrigin / texel_size); out_AO = 1.0; while(true){ vec3 ray = origin + t * dir; vec4 temp = projectionMatrix * vec4(ray, 1.0); vec2 texCoord = (temp.xy / temp.w) * 0.5 + 0.5; ivec2 newIndex = ivec2(texCoord / texel_size); if(newIndex != pixIndex){ float depth = texture(DepthMap, texCoord).r; float linearDepth = projAB.y / (depth - projAB.x); if(linearDepth > ray.z + 0.1){ out_AO = 0.2; break; } pixIndex = newIndex; } t += 0.5; if(texCoord.x < 0 || texCoord.x > 1.0 || texCoord.y < 0 || texCoord.y > 1.0) break; } } As you can see, here I just increment 't' by some arbitrary factor, calculate the 3D ray and project it to get the pixel coordinates, which is not really optimal. Hopefully, I would like to optimize the code as much as possible and compare it with shadow mapping and how it scales with the number of lights. PS: Keep in mind that I reconstruct position from depth by interpolating rays through a full screen quad.

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• How much is a subscriber worth?

  - by Tom Lewin

  This year at Red Gate, we’ve started providing a way to back up SQL Azure databases and Azure storage. We decided to sell this as a service, instead of a product, which means customers only pay for what they use. Unfortunately for us, it makes figuring out revenue much trickier. With a product like SQL Compare, a customer pays for it, and it’s theirs for good. Sure, we offer support and upgrades, but, fundamentally, the sale is a simple, upfront transaction: we’ve made this product, you need this product, we swap product for money and everyone is happy. With software as a service, it isn’t that easy. The money and product don’t change hands up front. Instead, we provide a service in exchange for a recurring fee. We know someone buying SQL Compare will pay us $X, but we don’t know how long service customers will stay with us, or how much they will spend. How do we find this out? We use lifetime value analysis. What is lifetime value? Lifetime value, or LTV, is how much a customer is worth to the business. For Entrepreneurs has a brilliant write up that we followed to conduct our analysis. Basically, it all boils down to this equation: LTV = ARPU x ALC To make it a bit less of an alphabet-soup and a bit more understandable, we can write it out in full: The lifetime value of a customer equals the average revenue per customer per month, times the average time a customer spends with the service Simple, right? A customer is worth the average spend times the average stay. If customers pay on average $50/month, and stay on average for ten months, then a new customer will, on average, bring in $500 over the time they are a customer! Average spend is easy to work out; it’s revenue divided by customers. The problem comes when we realise that we don’t know exactly how long a customer will stay with us. How can we figure out the average lifetime of a customer, if we only have six months’ worth of data? The answer lies in the fact that: Average Lifetime of a Customer = 1 / Churn Rate The churn rate is the percentage of customers that cancel in a month. If half of your customers cancel each month, then your average customer lifetime is two months. The problem we faced was that we didn’t have enough data to make an estimate of one month’s cancellations reliable (because barely anybody cancels)! To deal with this data problem, we can take data from the last three months instead. This means we have more data to play with. We can still use the equation above, we just need to multiply the final result by three (as we worked out how many three month periods customers stay for, and we want our answer to be in months). Now these estimates are likely to be fairly unreliable; when there’s not a lot of data it pays to be cautious with inference. That said, the numbers we have look fairly consistent, and it’s super easy to revise our estimates when new data comes in. At the very least, these numbers give us a vague idea of whether a subscription business is viable. As far as Cloud Services goes, the business looks very viable indeed, and the low cancellation rates are much more than just data points in LTV equations; they show that the product is working out great for our customers, which is exactly what we’re looking for!

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• Is there a problem with scrollTop in Chrome?

  - by Shaun

  I am setting scrollTop and scrollLeft for a div that I am working with. The code looks like this: div.scrollLeft = content.cx*scalar - parseInt(div.style.width)/2; div.scrollTop = content.cy*scalar - parseInt(div.style.height)/2; This works just fine in FF, but only scrollLeft works in chrome. As you can see, the two use almost identical equations and as it works in FF I am just wondering if this is a problem with Chrome? Update: If I switch the order of the assignments then scrollTop will work and scrollLeft won't. <div id="container" style = "height:600px; width:600px; overflow:auto;" onscroll = "updateCenter()"> <script> var div = document.getElementById('container'); function updateCenter() { svfdim.cx = (div.scrollLeft + parseFloat(div.style.width)/2)/scalar; svfdim.cy = (div.scrollTop + parseFloat(div.style.height)/2)/scalar; } function updateScroll(svfdim, scalar, div) { div.scrollTop = svgdim.cy*scalar - parseFloat(div.style.height)/2; div.scrollLeft = svgdim.cx*scalar - parseFloat(div.style.width)/2; } function resizeSVG(Root) { Root.setAttribute("height", svfdim.height*scalar); Root.setAttribute("width", svfdim.width*scalar); updateScroll(svgdim, scalar, div); } </script>

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• Mathematically Find Max Value without Conditional Comparison

  - by Cnich

  ----------Updated ------------ codymanix and moonshadow have been a big help thus far. I was able to solve my problem using the equations and instead of using right shift I divided by 29. Because with 32bits signed 2^31 = overflows to 29. Which works! Prototype in PHP $r = $x - (($x - $y) & (($x - $y) / (29))); Actual code for LEADS (you can only do one math function PER LINE!!! AHHHH!!!) DERIVDE1 = IMAGE1 - IMAGE2; DERIVED2 = DERIVED1 / 29; DERIVED3 = DERIVED1 AND DERIVED2; MAX = IMAGE1 - DERIVED3; ----------Original Question----------- I don't think this is quite possible with my application's limitations but I figured it's worth a shot to ask. I'll try to make this simple. I need to find the max values between two numbers without being able to use a IF or any conditional statement. In order to find the the MAX values I can only perform the following functions Divide, Multiply, Subtract, Add, NOT, AND ,OR Let's say I have two numbers A = 60; B = 50; Now if A is always greater than B it would be simple to find the max value MAX = (A - B) + B; ex. 10 = (60 - 50) 10 + 50 = 60 = MAX Problem is A is not always greater than B. I cannot perform ABS, MAX, MIN or conditional checks with the scripting applicaiton I am using. Is there any way possible using the limited operation above to find a value VERY close to the max?

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• Reinforcement learning toy project

  - by Betamoo

  My toy project to learn & apply Reinforcement Learning is: - An agent tries to reach a goal state "safely" & "quickly".... - But there are projectiles and rockets that are launched upon the agent in the way. - The agent can determine rockets position -with some noise- only if they are "near" - The agent then must learn to avoid crashing into these rockets.. - The agent has -rechargable with time- fuel which is consumed in agent motion - Continuous Actions: Accelerating forward - Turning with angle I need some hints and names of RL algorithms that suit that case.. - I think it is POMDP , but can I model it as MDP and just ignore noise? - In case POMDP, What is the recommended way for evaluating probability? - Which is better to use in this case: Value functions or Policy Iterations? - Can I use NN to model environment dynamics instead of using explicit equations? - If yes, Is there a specific type/model of NN to be recommended? - I think Actions must be discretized, right? I know it will take time and effort to learn such a topic, but I am eager to.. You may answer some of the questions if you can not answer all... Thanks

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• sample java code for approximate string matching or boyer-moore extended for approximate string matc

  - by Dolphin

  Hi I need to find 1.mismatch(incorrectly played notes), 2.insertion(additional played), & 3.deletion (missed notes), in a music piece (e.g. note pitches [string values] stored in a table) against a reference music piece. This is either possible through exact string matching algorithms or dynamic programming/ approximate string matching algos. However I realised that approximate string matching is more appropriate for my problem due to identifying mismatch, insertion, deletion of notes. Or an extended version of Boyer-moore to support approx. string matching. Is there any link for sample java code I can try out approximate string matching? I find complex explanations and equations - but I hope I could do well with some sample code and simple explanations. Or can I find any sample java code on boyer-moore extended for approx. string matching? I understand the boyer-moore concept, but having troubles with adjusting it to support approx. string matching (i.e. to support mismatch, insertion, deletion). Also what is the most efficient approx. string matching algorithm (like boyer-moore in exact string matching algo)? Greatly appreciate any insight/ suggestions. Many thanks in advance

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• LaTex, align alignment characters between align blocks

  - by ccook

  I would like to align two alignment characters between two align blocks so that I can have some text in the middle of a derivation with equations maintaining the horizontal alignment. For example the following excerpt of latex using align \begin{align*} \frac{\delta \phi}{\delta x_1} = {} &\frac{9}{8}\frac{\delta_1\phi}{\delta_1x_1}-\frac{1}{8}\frac{\delta_3\phi}{\delta_3x_1} \\ & \frac{9}{8}\frac{1}{h_1}\left[\phi(x_1+h_1/2)-\phi(x_i-h_1/2)\right]-\frac{1}{8}\frac{1}{3h_1}\left[\phi(x_i+3h_1/2)-\phi(x_1-3h_1/2)\right] \end{align*} some text in the middle \begin{align*} & \frac{9}{8}\frac{1}{h_1}\left[\phi(x_1+h_1/2)-\phi(x_i-h_1/2)\right]-\frac{1}{8}\frac{1}{3h_1}\left[\phi(x_i+3h_1/2)-\phi(x_1-3h_1/2)\right] \end{align*} Ideally I would like the left of the equation in the second block to line up with that of the second equation in the first block. I could do a workaround by not having text in the middle, however, I would like this functionality. EDIT I would like to have a good amount of text between. Say three to four lines that line up as normal paragraphs. Adding text in the alignment block is the workaround I poorly alluded to.

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• Confused over behavior of List.mapi in F#

  - by James Black

  I am building some equations in F#, and when working on my polynomial class I found some odd behavior using List.mapi Basically, each polynomial has an array, so 3*x^2 + 5*x + 6 would be [|6, 5, 3|] in the array, so, when adding polynomials, if one array is longer than the other, then I just need to append the extra elements to the result, and that is where I ran into a problem. Later I want to generalize it to not always use a float, but that will be after I get more working. So, the problem is that I expected List.mapi to return a List not individual elements, but, in order to put the lists together I had to put [] around my use of mapi, and I am curious why that is the case. This is more complicated than I expected, I thought I should be able to just tell it to make a new List starting at a certain index, but I can't find any function for that. type Polynomial() = let mutable coefficients:float [] = Array.empty member self.Coefficients with get() = coefficients static member (+) (v1:Polynomial, v2:Polynomial) = let ret = List.map2(fun c p -> c + p) (List.ofArray v1.Coefficients) (List.ofArray v2.Coefficients) let a = List.mapi(fun i x -> x) match v1.Coefficients.Length - v2.Coefficients.Length with | x when x < 0 -> ret :: [((List.ofArray v1.Coefficients) |> a)] | x when x > 0 -> ret :: [((List.ofArray v2.Coefficients) |> a)] | _ -> [ret]

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• Mathematics for Computer Science Students

  - by Ender

  To cut a long story short, I am a CS student that has received no formal Post-16 Maths education for years. Right now even my Algebra is extremely rusty and I have a couple of months to shape up my skills. I've got a couple of video lectures in my bookmarks, consisting of: Pre-Calculus Algebra Calculus Probability Introduction to Statistics Differential Equations Linear Algebra My aim as of today is to be able to read the CLRS book Introduction to Algorithms and be able to follow the Mathematical notation in that, as well as being able to confidently read and back-up any arguments written in Mathematical notation. Aside from these video lectures, can anyone recommend any good books to help teach someone wishing to go from a low-foundation level to a more advanced level of Mathematics? Just as a note, I've taken a first-year module in Analytical Modelling, so I understand some of the basic concepts of Discrete Mathematics. EDIT: Just a note to those that are looking to learn Linear Algebra using the Video Lectures I have posted up. Peteris Krumins' Blog contains a run-through of these lecture notes as well as his own commentary and lecture notes, an invaluable resource for those looking to follow the lectures too.

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