▪ Strict durability means that as soon as a transaction is committed, the server writes the information to the transaction log file.
▪ Relaxed durability means that the server might not write the information as soon as the transaction is committed; instead, the server might wait, for example, until it is less busy or until it can write multiple transactions in a single write operation.
If you can afford to lose a small amount of recent data, and if performance is crucial to you, use relaxed durability. Relaxed durability is appropriate when each individual transaction is not crucial. For example, if you are monitoring system performance and you want to store data on response times, you might only be interested in average response times, which will not be significantly affected if you are missing a few pieces of data. Since measuring performance will itself affect performance (by using up resources such as processor capacity and I/O bandwidth), you probably want your performance tracking operations themselves to have high performance (low cost) rather than high precision. Relaxed durability is appropriate in this situation.
On the other hand, if you are tracking financial data, such as bill payments, you probably want to ensure that 100% of your committed data is stored and recoverable. In this situation, use strict durability.
If you are not sure whether strict or relaxed durability is appropriate, use strict durability.