System manufacturers use different types of SSD caching, such as the following:
Write-through SSD caching:
The system writes data to the SSD cache and to the primary storage device at the same time. Data is not available from the SSD cache until the host confirms the write operation is complete at both the cache and the primary storage device. Write-through SSD caching can be cheaper for a manufacturer to implement because the cache does not require data protection. A drawback is the latency associated with the initial write operation.
Write-back SSD caching:
The host confirms a data I/O block is written to the SSD cache before the data is written to the primary storage device. Data is available from the SSD cache before the data is written to primary storage. The advantage is low latency for both read and write operations. The main disadvantage is the risk of data loss in the event of an SSD cache failure. Vendors using a write-back cache typically implement protections such as redundant SSDs, mirroring to another host or controller, or battery-backed RAM.
Write-around SSD caching:
The system writes data directly to the primary storage device, bypassing the SSD cache. The SSD cache requires a warmup period, as the storage system responds to data requests and populates the cache. The response time for the initial data request from primary storage will be slower than subsequent requests for the same data served from the SSD cache. Write-around caching reduces the chance that infrequently accessed data will flood the cache.
Thank you!
