Write Through caching policy

Write-Through caching policy accelerates only reads.

This is how Write-Through caching works in VirtuCache. When a block is first read by VMware from backend storage, VirtuCache immediately copies it to in-host cache media. When the block is requested again by VMware, VirtuCache now serves it from the in-host cache. As the cache media fills up, the least recently used and the least frequently used reads are evicted from the cache device to make room for new data. As a result, frequently and recently used reads are serviced from the in-host cache media, thus accelerating VM reads.

Regarding writes, all writes from VMware are synchronously written to both the VirtuCache cache media and backend storage. As a result, writes are not explicitly accelerated. Write performance is improved only to the extent that the reads are offloaded to in-host cache, which then frees up SAN resources to service writes better.

In the case of a host failure, read and write cache are lost, but there is no data loss because both reads and writes are on the backend storage in any case.

Write-Through caching policy does not explicitly improve write performance. If you want to improve the performance of both reads and writes, you should use Write-Back caching policy in VirtuCache.