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Solid-state drive caching has been around long enough that it has come to be thought of as more of a checklist item than a killer feature. As such, much of the attention surrounding the technology is now turning to improving SSD cache performance and reliability.
Initially, SSD caching was often based around a single disk. As the technology began to mature, vendors used multiple solid-state drives to increase SSD cache performance and prevent data loss.
A few years back, flash storage was considered to be somewhat unreliable because cells eventually wear out. Today, flash storage is just as durable -- if not more so -- as spinning media. Even so, flash drives do eventually fail. This isn't so much a problem for a read cache, but it can be a huge problem for a write cache. If a write cache is based on a single drive, and that drive fails, any uncommitted data will be lost. Vendors such as Synology have sought to address this SSD cache performance problem by mirroring the write cache to a second SSD. If the primary solid-state drive fails, the contents of the secondary SSD are immediately flushed. Write caching is also suspended to prevent data loss in case the second SSD were to fail.
Dennis Martin, president of Demartek, discusses the benefits of SSD cache performance as it relates to hot data.
From a performance standpoint, vendors have been working to maximize SSD cache performance throughput. Some use separate drives for read caching and write caching. Others use PCI Express-connected flash for cache storage. It has also become a common practice to stripe the cache across multiple SSDs as a way to overcome the bandwidth limitations of the disk controller and improve overall performance.
Using caching to increase SSD efficiency
Learn about the different types of caching
How to reduce write caching while increasing performance
Dig Deeper on Hybrid flash arrays
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