I am having doubt in SQL SERVER 2008 R2.?
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Hai everyone, I am new for SQL SERVER Administration. Nowadays i am looking for SQL Backup. I am very much confused about Differential & Transactional Log backups. Please explain me the difference step by step. Say suppose, my database name is X. I have full backup at 10am. i made some changes then i took backup(Differential) at 11am. I made some changes, then i took Transactional Backup at 11.30am. I made some changes, sharply at 1pm my database has been corrupted. Finally i have the following backup. 10am FullBackup 11am Differential Backup 11.30am Transactional Backup Now how can i restore the above backup(i mean which one first, second, third). The thing i need to get data till 1am(i mean without data loss). Please explain me.
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Answer:
A Differential Backup contains all changes to the database since the last Complete Backup. Transaction Log backup contains all changes since the last Transaction Log backup OR Complete Backup (if no Log Backup has taken place yet since the last Complete backup). You typically perform an occasional Complete Backup, and either Transaction Log OR Differential backups that can be run more frequently since they are smaller than a Complete backup. In your scenario, you could restore the 10am Full Backup, then the 11:30 Transactional Backup, but you would still be missing the data from 11:30 to 1. Transactional backups are small since they only contain the data modified since the last Transactional backup, so you could run these jobs every 5 minutes, and a full backup once a day. If you fail a 1am, you would restore the 10am Full Backup, then sequentially restore the 180 Transactional backups that took place between 10am and 1am (you can apply multiple backups at once). Or, you could run a Differential Backup every 5 minutes, and overwrite the previous Differential backup since all transactions are backed up (since the last Complete backup) with every Differential backup. The size of the database, update frequency, and other concerns will dictate which approach is better. Also, if zero data loss is crucial, you may also want to look at Database Mirroring, Failover Clusters, Log Shipping, and Replication.
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Other answers
To answer in simple; this totally depends on what RECOVERY MODEL you have set. As long as you have set the to FULL - then in anytime of disaster, just restore the ACTIVE transaction log to recover the data till to the point. In addition: 10AM and 11AM backup is good only if your database is corrupted is such a way that recovering becomes impossible then you can go back to the previously best available full backup with the consequences of the data loss (lets say, in your case minimal)
Raghavendra Mudugal
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