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Cache concepts and cache techniques

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The concept of the Cache memory has been around since long time. Cache memory is generally used to fill the performance gap between computing architecture and persistent storage. Persistent bulk storage units cannot keep up with the performance requirements that of Compute processing. Just take an example of RAM to understand performance gap of CPU and Disk. Why do we need RAM?

Cache can be hardware or software component that stores data in it so that future requests for the data can be served using data stored in cache instead of re-computing or fetching from Persistent storage for each operation.

During read operations, if the requested data is found in a cache, It is called as Cache Hit and data is loaded from cache only as there is no need to load all the way from Persistent layer. In case, requested data is not found in cache and needs to recompute or be fetched from persistent storage, it is called as Cache Miss.

As mentioned earlier, cache can be hardware or software component. Also cache can be used at various levels in computing architecture.  Below are some of the examples of hardware and software cache based on their usage at various levels.

Hardware Cache:

Software Cache:

Caching Benefits:

Caching Techniques:

There are three main caching techniques that can be deployed. Each method comes with its pros and cons.

Write Through:

Write Around:

Write Back:

Relating above information in VMware vSphere virtualization, vSphere has features like vFRC, vSAN that uses cache mechanism. vFRC supports write-through or read caching whereas VMware vSAN uses Write back caching mechanism.

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