SSD cache can be worth it on Synology when your workload has frequent access to randomly placed data, especially re-read patterns such as mail servers and file services. It is also likely to help with:
- File server usage with many concurrent users and small files
- iSCSI and Fibre Channel storage
- Synology Virtual Machine Manager
- Database storage
- Snapshot
- Webserver
- Regular backup tasks with Synology Active Backup for Business
- Mail services
It is less useful for large sequential read/write workloads, such as HD video streaming, and for entirely random data reading patterns.
How to add and configure it correctly:
- Check whether your Synology NAS supports SSD cache.
- Use SSDs that are compatible with your Synology storage system and are on the Synology Products Compatibility List.
- Use SSDs in Healthy status.
- Use SSDs of the same drive type.
- Use no more than six SSDs per cache group.
- A read-only cache requires at least one SSD.
- A read-write cache requires at least two SSDs.
- The target volume must be in Healthy status and cannot be running other tasks.
- For best sizing, run Storage Manager > Storage > SSD Cache Advisor for at least seven days before creating the cache.
- Memory matters: every 1 GB of SSD cache requires approximately 400 KB of system memory, and the system will only use up to 25% of the pre-installed system memory for SSD cache creation.
- If the storage pool does not already contain a cache group, DSM will guide you to create both a cache group and an SSD cache.
Notes:
- SSD cache algorithms, performance, and features are continuously improved with each new DSM version, so keeping the SSD cache version up to date is recommended.
- If your SSD caches were created in previous DSM versions, you may want to remove them and create new ones.
Sources used: [9], [10], [11], [12], [15], [16]