Sunday, May 1, 2016

Database disaster prevention by Olek Nilson (Microsoft SQL)

Disclamer: This article was taken from DineSQL blog and this post is written by Olek Nilson. All credit goes to them.

Database disaster prevention is one of the greatest pains in life of every DBA. Data from database are changing daily, gradually expanding the size of the latter. Of course, there is no perfect way to prevent database corruption, but there are some practical steps that can help you to bring the risk to minimum.

It’s important to say a few words about Microsoft Corporation. In spite of the fact that SQL Server is 100% Microsoft product, the company does not provide any means to protect your database, meaning that database protection completely up to the user.

Below we would like to discuss cases that can trigger database disaster.

One of the most popular cases that can potentially cause database corruption is hardware failure, for example, incorrect work of Disk, CPU or Memory Module.

Another thing that can corrupt your database is Antivirus software. Please note that after your antivirus software is installed, all SQL Server Database Files should be excluded from being scanned by the Antivirus software.

The next issue that can potentially damage your database is a desire to save free space on the local disk. Based on my personal experience, there were some users who stored all SQL Server database files in zip or 7zip files to save some space on their disks. Ultimately, these actions lead to a database failure. If you desperately need free space, you can use third party tool to make database backups with compression and store them online.

Another important thing that will help you to prevent database disaster is setting up the latest updates for SQL Server and Windows. Otherwise it will cause incorrect working of your shift.  

And do not forget about the case with a power failure that may lead to all databases being corrupted.

It is not an exhaustive list of failures that can destroy your database. So what shall we do to prevent database disasters and minimize the risk? You have to remember that there is no perfect way or method that will ensure 100% protection for your database. However, the best thing that can help you to minimize the risk of the database corruption is to make scheduled database backups. Database backups cannot prevent the corruption, but they can help you to restore the database with minimal losses.   

It is recommended that all experienced DBAs should make regular database backups. This leads to a question  – How often should I make backups or what backup strategies should I employ? Before answering this question, please consider yet another question - How much data can you afford to lose? Working as a DBA, I have had a great many databases to restore and I can say that the more quality backups you have the less data you will eventually lose. 

Presently there are three ways to make database backups:
  1. Using T-SQL commands:

    If you prefer using T-SQL command you have to keep in mind that you need to make database backups all the time. Even you have to create a schedule and carefully stick to it. Perhaps, make backups with the help of T-SQL commands are comfortable if the database is not large and grows slowly. But in the most cases changes in the database are taking place all day and night, so how do make backups at night? Of course, to solve this issue you can find in the Web scripts for making schedule backups.

    So, if you make the decision to make database backups with the help of T-SQL use the following commands:
    -- To make a full database backup use the following command:
    BACKUP DATABASE AdventureWorks TO DISK = 'Z:\SQLServerBackups\AdventureWorks.bak'
    -- Use the following command to make a differential backup:
    BACKUP DATABASE AdventureWorks TO DISK = 'Z:\SQLServerBackups\AdventureWorksDiff.bak' WITH DIFFERENTIAL
    -- The following command will help you to make a transaction log backup:
    BACKUP LOG AdventureWorks TO DISK = 'Z:\SQLServerBackups\AdventureWorksLog.bak'
  2. With the help of SSMS (SQL Server Management Studio):

    Using SSMS for making backups is a little bit easier then make backups with the help of T-SQL commands. You don't need to write commands every time when you are going to make a backup it is enough to make a couple simple steps, which we described below. It has to be admitted that you can also make scheduled backups with the help of SSMS, but it will take more efforts from you.

    To make a backup please:
    a. Right-click on the database you want to backup
    b. Select “Tasks”, then “Back up…”
    c. Choose “Backup type"
    d. Add backup destination
    e. Click “OK”
  3. Or use third party tools; You can choose such enterprise solutions as SQL Backup Pro from RedGate, something similar to SqlBackupAndFtp, or try out if you prefer SAAS model.
In my opinion, this is the best way for making scheduled database backups. Here everything you need is to create the job for the scheduled backups and run the application. The third party tool will make backups according to the schedule.

     So, if your databases are growing fast and there are many changes occurring every hour, it would be better to choose “maniacal” backup plan, for example, it is a Full database backup every 24 hours, a Differential backup every three hours and make transaction log backups every 15 minutes. Yes, perhaps it will take more time to restore your database should failure occur, but the percentage of data loss will be minimal.

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