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When to Use Mirroring as a Data Recovery Solution

Posted by Lana Tkachenko on Wed, Nov 02, 2011

Mirroring as a Data Recovery SolutionSo far we have discussed tape backup, snapshot backup and data replication as examples of data recovery solutions. Each of these methods copy data on a computer in case a disaster recovery is necessary. Mirroring is another type of data recovery solution that is often used to create multiple drives with the same information. It works by linking two systems together that will continually match each other. For example, when “File A” is created on a computer, it will be saved on two separate disks at once. Mirroring is used for a variety of reasons—for data backup, for faster downloads in different geographic locations, and to balance a server load.

Mirroring can occur in two regards: on disks, or on server. RAID (Redundant Array of Independent Disks), is an example of mirroring that is stored on two separate physical disks in order to ensure that the data is always available. Mirrored data can also be stored on two different servers in two separate locations. This is done so that the same information is quickly accessed at various sites.  

If a computer malfunctions and disaster recovery must be initiated, mirrored solutions work through a hot swap system or a hot standby disk system in order to save data. In a hot swap system, the system itself signals a disk failure and switches over to the mirrored disk. Users frequently do not even know that this was done, except for an alert that may pop up on their screen.

Hot standby is a more sophisticated system during which a backup occurs from the active disk onto the remaining disk. Then, a new disk is installed creating a new backup system, while the malfunctioning disk is discarded. During this process, little data is lost and minimum disruption occurs. With mirroring, data recovery can be performed swiftly and rapidly.

Let’s look at the other pros and cons.


  • Database mirroring is robust and efficient because the changes synchronize without any lag or data loss.
  • Mirroring requires less bandwidth than other methods of replicating data. Also, replication is not limited by geography so servers located far away can mirror each other.
  • No special hardware or cluster hardware is required to support database mirroring, which means that it has a lower infrastructure cost than other backup methods.
  • Database mirroring allows for real time data security because the data is written to two drives at the same time.
  • Because data is always copied onto a second drive, backup can be performed quickly and easily without slowing down productivity.
  • Mirroring delivers a high degree of protection against disk failure.


  • Database mirroring is limited to two (2) servers.
  • The downside of real time data security is that if the user incorrectly changes a vital aspect of the Operating System, the backup is affected as well.
  • Because backups occur frequently during mirroring, the second drive receives a lot of wear. Also, mirroring adds some extra load on the principal server because its function is to keep the database mirror synchronized.
  • Mirroring can lead to less storage space for data, because both drives need to have enough space to support the entire hard drive.
  • Having multiple disks with the same information may arouse a false sense of confidence that can lead to poor backup maintenance. Disk mirroring does not prevent against viruses, filed deletion, and other logical loss of data.
  • Additional cooling is required when adding a second disk, otherwise the temperature inside the case may get too hot and the disk could be ruined.
  • If database mirroring is removed for some reason, the whole process of configuring mirroring has to be completely redone.

After weighing the pros and cons of mirroring, it is important to determine whether a situation calls for it as a backup recovery solution. If using it as a way to backup a single computer drive or server, mirroring can be quite successful. If the intention is to back up many computers, the process can get more expensive and time consuming. Mirroring is also a good option for storing sensitive data because a copy of the data always exists in an easily-accessible location.  However, somebody looking for a backup recovery system without needing to document every instance of data change may want to chose simpler backup recovery software, such as snapshot backup.

 True Cost of Downtime



Tags: Disaster Recovery, Business Continuity

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