What Is a Write-Back Cache?

A write-back cache stores a write in the cache and reports success right away, then flushes the change to the underlying store asynchronously. This keeps writes fast and can batch many updates into fewer backing-store operations. The trade-off is that data buffered in the cache can be lost if the cache fails before it flushes.

Why it matters

Write-back lowers write latency and backing-store load, which suits write-heavy workloads. But because acknowledged data may not yet be durable, it needs care where loss is unacceptable, unlike a write-through cache.

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