Sql server recovery models and backup types « sql server blog forum

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Sql server recovery models and backup types « sql server blog forum

  1. 1. 27/08/2012 SQL server Recovery Models and Backup types « Sql server Blog Forum Sql server Blog Forum Backup/Restore SQL server Recovery Models and Backup types SQL server Recovery Models and Backup types by Muthukkumaran kaliyamoorthy Published on: June 7, 2011 C omments: 21 C omments Tags: Recovery models importance, SQL RPO RTO, SQL server Backup types, SQL server Recovery Models C ategories:Backup/Restore, Basics for freshers, Internals In this post I am going to explain the importance of recovery models and backup types. Why I am writing this post ? Because, when I was teaching about the topic to my PHP friend .He got doubts on bulk logged recovery model and differential backups. I have given some examples and cleared his doubts. I am going to share this with you guys too. I hope this will help for Freshers and DBA managers. Recovery models and backup types are important to plan the recovery point objective (RPO) and recovery time objective (RTO). We can’t differentiate the recovery models and backup types. Simply it’s a mixture. Let’s see the discussion. Manager: We need minimum data loss and downtime. DBA: The existing system has low disk space and the transaction log backups are failing often. We need more disk space to do this, Sir! Manager: I asked about this to management they will give soon, until you will do something with your DBA knowledge. DBA: C hanging the recovery models full to simple and back to full and shrinking the log file daily. The DBA send an email to his manager. The shrinking is not best practices, Sir! Manager: ??? Let’s come to the point. Recovery Models SQL server has three types of recovery models. 1. Full 2. Bulk Logged 3. Simple Full In full recovery model all the database operations are fully logged. This means all the modifications have written fully to the log file. The full recovery model is always the best one for production servers. In the full recovery model we can take all kinds of backups like full, differential, transaction Log and point in time recovery (PTR) too. Bulk Logged The name itself you can understand the answer. Bulk operations minimally logged in this mode. This means it has written only minimal roll backing information to the log file not whole (i.e. not fully logged). The BCM page contains all the required information. See an example you can understand. Bulk logged recovery model is the best model for server performance. Because all the bulk changes havewww.sqlserverblogforum.com/2011/06/sql-server-recovery-models-and-backup-types/ 1/5
  2. 2. 27/08/2012 SQL server Recovery Models and Backup types « Sql server Blog Forum been written minimally (Not fully) to the transaction log file. In bulk logged recovery model we can take all kinds of backups like full, differential and transaction Log but, the drawback is the point in time recovery (PTR)is not possible, when there is a bulk operations have done with the transaction log file. Keep in mind, in full and bulk logged recovery model the log files grow bigger until the BAC KUP LOG has done. For more clarity. See an example: Just assume 5,000 bulk operations have written in 8000 pages. In full recovery model each 5,000 bulk operations have written in 8000 pages, because all the changes have written fully in the full recovery model. But when we used bulk logged recovery model, it has written 1000 pages only ,Because SQL server has written the bulk changes to an extent wise not the page wise i.e. minimally logged operation (8 pages = 1 extent). It will help to improve the overall server performance. Now you know, Writing 8000 pages are good or 1000 pages. Note: This bulk logged model is good only for the bulk operations. Simple The name itself you can understand the answer. Simple recovery model is just simple this means SQL server will run the checkpoint every minute and truncate the transaction log file often. Mostly the log file will not grow larger. Most of the time the simple recovery model is a good choice for non production servers. Because the log file will not grow larger. Also we would not take log backups. (If you’re planning to take the log backup then don’t put in simple) In the simple recovery model the transaction log backup is not possible. We can take full and differential backups only. Now you could know answer for the following questions. What is the use of Full, Bulk logged and Simple recovery model. Which one is best? Backup Types SQL server has number of backup types. Here I am going to explain the main three types. 1. Full 2. Differential 3. Transaction log I recommend to read Paul S Randals’s backup survey post. http://www.sqlskills.com/BLOGS/PAUL/post/Importance-of-having-the-right-backups.aspx Full backup A full backup backs up the full/whole database. That backs up all the committed data. The full database backup has been done in all the recovery models. Differential backup A differential backup only backs up the changed data/extents that were modified after the full database backup has done. The DCM has tracked all the changed extents. The differential backup has been done in all the recovery models. For more clarity. See an example: Assume we are scheduled every Sunday full backup @12 am and daily differential backup 10 PM. Note: The data change daily 500 MB. Question: How much data got back up on Thursday? The student answers 500 MB. As I already told, differential database backup “backs up all the data that has changed since the last full database backup”. The answer is, Monday 500MB + Tuesday 500 MB + Wednesday 500MB + Thursday 500MB= 2000MBwww.sqlserverblogforum.com/2011/06/sql-server-recovery-models-and-backup-types/ 2/5
  3. 3. 27/08/2012 SQL server Recovery Models and Backup types « Sql server Blog Forum Edit: I added these lines after I had replied the forum question SSC . So the differential backup on Thursday has all the data. That is (Monday+Tuesday+Wednesday+Thursday). It helps to bring the database online as quickly as possible. Transaction log backup A transaction log backup backs up the transaction log file. That is all the modifications/changes. The transaction log backup only possible in full and bulk logged recovery model. The transaction log backup is important to minimize data loss and log file size too. It’s very important to keep the transaction log backup as much as safe, because the restoration needs the sequence of the transaction log backup if, you deleted/missing any one of the backups then you can’t recover the whole data. I have suggested running the log backups often. It will reduce the log file size and helps to minimize your data loss. Question: How to restore the database after a disaster? (OR) What is the sequence to restore the database? Answer: Restore a full backup and followed by recent differential backup and all the log backup one by one in a sequence. For more clarity. See an example: Assume we are scheduled every Sunday full backup @12 am and daily differential backup 10 PM and an hourly log backup. The database crashed on Wednesday at 1:30 PM. Then the restoration will be on Sunday full backup+ Wednesday differential backup (Most recent) + log backup @11+@12+@1. Believe me guys, Test your backups often and keep at least two copy of the full backups safely, Because the full backup is important to restore the all other backups. This means without a full backup you can’t restore the differential and log backups. Muthukkumaran kaliyamoorthy I’m currently working as a SQL server DBA in one of the top MNC . I’m passionate about SQL Server And I’m specialized in Administration and Performance tuning. I’m an active member of SQL server C entral and MSDN forum. I also write articles in SQL server C entral. For more Click here More Posts - Website Share this 21 C omments - Leave a comment ram June 7, 2011 at 11:22 am dude,superb , very useful to understand the basic recovery model and backup types and the way which you explained s nice Muthukkumaran June 7, 2011 at 12:01 pm I wrote this post after we had a class discussion. Thanks to you dude. Anonymous June 7, 2011 at 3:43 pm Hi Muthu 1. As you said, In-case of any disaster on Wednesday @ 1:30 pm. 2. We have to perform the "Tail-Log" backup first. Then only we will have last 30 minutes transaction after the actual transaction-log hourly backup. correct ? 3. Then, we have to proceed with further Restore either (Norecovery or Standby state) Muthukkumaran June 8, 2011 at 6:01 am @Anonymous user Yep, You are right.we can take the tail log backup if, there is no damage in transaction log file.I didnt focus the restore part fully. Its just an example to understand the restoration sequence to all the newbies.www.sqlserverblogforum.com/2011/06/sql-server-recovery-models-and-backup-types/ 3/5
  4. 4. 27/08/2012 SQL server Recovery Models and Backup types « Sql server Blog Forum Thanks to reading my posts. i dont know most of my comments are from Anonymous user. Nobody is writing his name. Anonymous June 9, 2011 at 11:40 am Spot-on post.I agree with the first person comment the way you explained really superb and its written using very simple/understandable english. keep up the good work. Great examples. BY Yardy Muthukkumaran June 9, 2011 at 5:31 pm @yardy glad you liked it.thanks To be frank i don’t know complex words.lol vinoth June 11, 2011 at 6:21 am Hi muthu, Great post. I liked this. Monday 500MB + Tuesday 500 MB + Wednesday 500MB + Thursday 500MB= 2000MB Muthukkumaran June 21, 2011 at 9:13 am So the differential backup on Thursday has all the data. That is (Monday+Tuesday+Wednesday+Thursday). It helps to bring the database online as quickly as possible. I have added these lines after i replied the forum question http://www.sqlservercentral.com/Forums/Topic1128012-391-2.aspx?Update=1 Anonymous July 9, 2011 at 9:36 am H Muthu, I am new to SQL DBA group. I have doubt here about DR, as you said the DB crashed on Wed at 1:30 PM Below is the sequential backup i have backup: Sun – Full backup @ 12:00 AM (Mid-Night) Mon – Differential Backup @ 10: PM (Night) Tue – Diff @ 10:PM (Night) Wed – DB crashed @ 1:30 PM (Afternoon) Than my question here is how come we follow restore with – Sun full backup + WED Diff because if DB crashed at 1:30 PM (Noon) on wed thn we dont have WEDs diff backup (night)as DB crashed in Noon. So do we need to add tuesdays Differentail Backup. Please clarify my doubt. thanks- Pooja Muthukkumaran July 9, 2011 at 10:55 am Pooja, Yep you are right. If you have log backup you can restore that too. If you want more answer I suggest you to ask questions to SQlservercentral and MSDN forum. this post is quoted by SQL server Disaster Recovery plan « SqlserverBlogForum 9, 2011 at 2:19 pm October [...] its simple(less expensive) and good option for disaster recovery but it’s depends upon your backup strategy and recovery model. The backup restore will work for all the above three DR methods. The DBA job is keep the data [...] this post is quoted by Difference between truncating and shrinking the transaction2011 file « pm October 9, log at 3:34 SqlserverBlogForum [...] It depends upon the recovery model. [...] Myrman October 31, 2011 at 1:04 am Thank you for making your work very easy to comprehend. The topic is somewhat baffling as it is but you make it look easy. This is just what people need to read.www.sqlserverblogforum.com/2011/06/sql-server-recovery-models-and-backup-types/ 4/5
  5. 5. 27/08/2012 SQL server Recovery Models and Backup types « Sql server Blog Forum Muthukkumaran kaliyamoorthy October 31, 2011 at 7:23 pm Glad you liked it.Thanks. Deandrea Nodine November 3, 2011 at 10:29 pm Useful page and incredibly informative. Thanks for taking the time to write it and post it! Muthukkumaran kaliyamoorthy November 4, 2011 at 11:35 am Thanks Deandrea Nodine. Mellie Partible November 6, 2011 at 8:51 am You, my friend, ROC K! I found just the info I already searched everywhere and just could not locate it. What a perfect website. I have bookmarked your website: http://www.sqlserverblogforum.com/2011/06/sql-server-recovery-models-and-backup-types/ and will check back often. Thanks for the awesome information! Muthukkumaran kaliyamoorthy November 6, 2011 at 11:01 am I’m glad you liked it. Dee Lazich February 11, 2012 at 12:58 am I don’t even understand how I finished up right here, however I assumed this publish was once great. I do not recognize who you might be however certainly you’re going to a well-known blogger should you are not already C heers! Muthukkumaran kaliyamoorthy February 11, 2012 at 11:26 am I’m glad it helps you. Thanks Dee. this post is quoted by Server Data Recovery | Data Recovery May 18, 2012 at 10:48 am [...] Server Data Store for Distribution Perform these steps for both servers: 1. … Fetch C ontent Two- phase C ommit Protocol – Wikipedia, The Free EncyclopediaTo accommodate recovery from failure (a… sform:capitalize;">Two-phase C ommit Protocol – Wikipedia, The Free EncyclopediaTo accommodate [...] © 2 0 1 2 Sql server Blog Forum A ll rights res erved - P owered by WordP res swww.sqlserverblogforum.com/2011/06/sql-server-recovery-models-and-backup-types/ 5/5

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