Identify which drive tier supplies the Storage Spaces Direct cache

Source facts

Storage Spaces Direct automatically allocates the fastest drive type to caching when a deployment contains different drive types; the remaining drives supply capacity. Cache behavior depends on the capacity media. Flash capacity receives write caching, while rotating-disk capacity receives both read and write caching. Microsoft describes this server-side cache as persistent and configured automatically during deployment, with little manual management normally required. Microsoft documentation.

Applicability

Record the actual drive types and roles on each server. Distinguish this persistent storage-pool cache from the separate CSV memory read cache and from the standalone Storage bus cache feature.

DSE recommendation

Prepare a drive-role inventory that identifies cache media, capacity media, and the intended workload. Have the storage owner review whether the observed roles match the hardware design. Before changing media or cache settings, record the current configuration and define a workload-specific evaluation plan.

Verification

Compare the reported cache and capacity assignments with the approved inventory. Measure the chosen workload under controlled conditions and keep the test duration and input load with the results. Investigate uneven device assignments or unexpected latency without assuming that the presence of a cache proves an application performance target.

Official references

Microsoft Learn: Understanding the storage pool cache in Azure Local and Windows Server clusters. Source reviewed September 8, 2026.