Overview

SSD cache can accelerate small random reads or writes on HDD volumes when the working set fits within cache size.

It is not a replacement for a full SSD volume when low latency is required across all data.

When SSD cache helps

Look for workloads with hot subsets of data and many small operations.

• Catalogs and previews for photo libraries
• Small files and indexes for team projects
• VM metadata and application temp files

Cache types and media

Choose read only or read write cache based on risk and workload.

• Read only cache - lower risk and simple to deploy
• Read write cache - faster writes but requires safe shutdown and good power conditions
• Use NAS or data center grade SSDs with sustained write endurance

Sizing the cache

Size to cover the active working set rather than the entire dataset.

• Start with 5 to 10 percent of the active data size
• Increase only if hit rates remain low after a learning period
• Keep spare capacity on SSDs to maintain performance

Setup steps

A short sequence keeps deployment predictable.

• Confirm slot compatibility and install SSDs
• Create read only or read write cache in Storage Manager
• Warm the cache by running typical workloads before measuring impact

Monitoring and tuning

Track hit rate and latency to verify benefits.

• Use performance graphs to watch cache hit rates
• Adjust cache mode or size if results are weak
• Revisit after DSM or application updates

Common pitfalls

Avoid these mistakes that reduce value.

• Using cache to hide failing disks or poor network paths
• Sizing too small for the active set
• Expecting cache to speed up large sequential transfers

FAQs

Short answers to common cache questions.

• Will cache help Plex streaming - not much for large sequential reads
• Do I need two SSDs - mirror pairs add resilience for read write cache
• Should I pick NVMe or SATA - pick what your model supports and size for endurance first