SSD Cache
SSD cache enhances performance where input-output (I/O) operations require frequent access to randomly placed data. It can thereby benefit predominantly re-read workload patterns, such as mail servers and file services. However, the benefits of using SSD cache are limited on certain workload patterns, in particular, large sequential read/write operations (e.g., HD video streaming) and entirely random data reading patterns.
Note:
- Find out if your Synology NAS supports SSD cache.
- We recommend using SSDs that are compatible with your Synology NAS and are on the Synology Products Compatibility List. Using SSDs not on the list may affect system stability and result in data loss.
SSD Cache Versions
SSD cache algorithms, performance, and features are continuously improved with each new DSM version. To ensure better feature support and performance, we recommend keeping your SSD cache version up to date. If your SSD caches are created in previous DSM versions, you may want to remove these SSD caches and create new ones.
Note:
- Removing an SSD cache may take several hours to complete depending on the amount of data stored on it. For detailed steps, refer to this article.
- An SSD cache is up to date if it does not display the Not the latest version field.
Cache Hit Rate
SSD cache by default only accelerates random I/O and does not accelerate sequential I/O. The Cache Hit Rate of an SSD cache can be calculated according to the following formula:
- Hit Rate of Read-Only Cache = Accelerated Random Read Counts / Total Random Read Counts * 100%
- Hit Rate of Read-Write Cache = Accelerated Random Read & Write Counts / Total Random Read & Write Counts * 100%