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SQL Server Disaster
An SQL (sequel) server disaster is an event where data loss occurs due to a natural disaster or something similar. Disaster recovery specialists are employed in order to place and exercise safeguards that protect against any major loss of data. These safeguards act as a disaster recovery system. A disaster recovery system consists of at least one or more of the following methods: Failover cluster, Database mirroring, Replication, Log shipping, and Backup and Restore. It also tends to involve a disaster recovery SQL server.
The Failsafe Cluster method keeps the SQL server’s data backed up on other servers so that it can be accessed whenever the main server goes down. This keeps the servers “high-availability,” active. High-availability refers to the amount of time a server system needs to be available for the people using it. Servers typically need to be available 24/7. Although, this method does involve a little “downtime,” or a period when the server isn’t active.
Database mirroring mirrors the main SQL server to another server. The two servers involved in this process are called “partners,” and one server always remains active while the other remains in standby. The active server sends information over to the passive server, which then copies the information onto itself. There are two different type of data mirroring: hot and warm.
Replication copies and distributes data from a primary server called “publisher” to secondary servers called “subscribers.” Subscribers are updated when the publisher is. This method can allow for load balancing and offline processing. There are three different types of replication: Merge, Snapshot, and Transaction. Merge involves both the publisher and subscriber being able to change data on the SQL. In case this leads to conflicting data, a merger agent steps in to correct things, updating everything to match the publisher. Snapshot involves the publisher making a copy of itself distributing it to the subscriber. Transaction involves an agent making changes to the subscriber so that it lines up with the publisher.
Log shipping automatically copies log transactions on the primary, or production, server and transfers it to the secondary “warm” server (“warm,” like the passive servers mentioned in data mirroring). The process moves in three steps: creating a transaction log copy, providing the secondary servers with this log transaction copy, and then updating the secondary servers to display the copy.
Finally, the Backup and Restore method. This one is basic and generally kept in the back pocket should other methods not work out. It involves two steps: backing up SQL server data and restoring SQL server data. Using this method involves sending the backup data offsite. Once it arrives at the offsite location, the backup is tested to make sure that none of the data is corrupted in any way. There are four different types of backup methods to choose from—full backup, partial backup, differential backup, and transaction log backup. How the data is handled offsite depends on the chosen backup method.
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