WriteThrough

Write-through caching is a data storage strategy in which every write to the cache is simultaneously written to the underlying storage. This approach keeps the cache and the backing store consistent at all times, reducing the risk of data loss if the cache is disrupted. The term is sometimes written as write-through or writethrough and is commonly discussed in the context of CPU caches, disk caches, and storage controllers.

How it works: When a write operation occurs, the cache is updated and the same data is immediately written to the next level of storage, such as main memory, a disk drive, or a remote storage array. Reads can still be served from the cache if the data is present; if not, the system retrieves the data from the backing store and caches it for subsequent accesses.

Advantages: The primary benefit is data durability and simpler recovery after a crash, since the most recent updates have been written to non-volatile storage. It also simplifies cache coherence in multi-level caching architectures and reduces the risk of stale data during failover.

Disadvantages: The main drawback is reduced write performance due to the need to perform writes to the backing store for every update. This can increase latency and bus traffic and may limit peak write throughput, especially on slower storage media.

Applications and notes: Write-through caching is favored in systems prioritizing data integrity and predictable durability, such as enterprise storage caches and servers with strict persistence requirements. It is often contrasted with write-back caching, which caches writes and delays updating the backing store to improve speed, at the cost of potential data loss on failure. In practice, implementations may vary in how strictly they enforce synchrony with the backing store.