Disaster Tolerance and Recovery in a Serviceguard Cluster
Disaster Tolerant Architecture Guidelines
Figure | Logical Data Replication |
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| Logical Replication |
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| in Software. |
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| No direct access to |
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| both copies of data. |
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•The distance between nodes is limited only by the networking technology.
•There is no additional hardware needed to do logical replication, unless you choose to boost CPU power and network bandwidth.
•Logical replication can be implemented to reduce risk of duplicating human error. For example, if a database administrator erroneously removes a table from the database, a physical replication method will duplicate that error at the remote site as a raw write to disk. A logical replication method can be implemented to delay applying the data at a remote site, so such errors would not be replicated at the remote site. This also means that administrative tasks, such as adding or removing database tables, has to be repeated at each site.
•With database replication you can roll transactions forward or backward to achieve the level of currency desired on the replica, although this functionality is not available with file system replication.
Disadvantages of logical replication are:•It uses significant CPU overhead because transactions are often replicated more than once and logged to ensure data consistency, and all but the most simple database transactions take significant CPU. It also uses network bandwidth, whereas most physical replication methods use a separate data replication link. As a result, there may be a significant lag in replicating transactions at the remote site, which affects data currency.
Chapter 1 | 43 |