With such mechanism, every consistent update to nonvolatile media will result in extra writes.For example, in Figure 1, in write-ahead logging, an update operation would (a) first write to the log, wait until the log is persistent, and then (b) update the correspondent locations according to the log.If we want to modify the structure to change it to store other people’s information, such as name: XYZ and age: 28, we have to update the two fields separately (as step 1 and step 2 in the example) due to the hardware limitation.If the system crashes right after we finished step 1 and before step 2, although the information in the data structure is not lost after rebooting, it is wrong and is not reusable now (state shown in the dashed box).Note: This guide works for upgrading Easy Tomato versions as well as for switching from other versions of Tomato or DD-WRT to Easy Tomato.Upgrading to the newest version of the Easy Tomato firmware is very easy.
During the installation, it is important to make sure that the router does not lose power.
Figure 1 shows an example of data consistency, if we have a data structure of people which contains two fields: name and age.
It is stored in NVRAM and its initial state is as Figure 1 shows.
Systems with NVRAM attaching to memory bus have been widely advocated  which would greatly facilitate the construction of in-memory durable data structures .
In such systems, persistent data structures reside in NVRAM as they are created and modified rather than being operated in one format and transformed into another format to be durable .