On Friday we discussed redundancy as a universal attribute of highly available (HA) components. See “’High Availability’ 101 – Redundancy.” This time we’ll explore data replication, an application of redundancy that is common in many HA systems.
Often, the first hurdle in creating an HA component involves accessing data in a highly available fashion. Unfortunately, it is also one of the most complicated and expensive problems to solve. Applying the principle of redundancy introduced on Friday, highly available data means redundant data. Redundant data requires the act of copying it to redundant locations. This copying is sometimes referred to as ‘replication’. Highly available data requires some form of replication. Complications may result from the potential overhead of this operation, and maintaining consistency between the disparate copies. Consistency is especially troublesome if the data is capable of being read and modified concurrently. Continue reading