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Get the most out of solid-state storage

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SSD enables tiering

Performance gains with solid-state storage technology aren’t limited to database applications. This is why we see an increased demand for caching and tiering solutions. Most servers -- whether singly or in groups -- are kept busy with a variety of application workloads, each having various busy times and slow times. If you have all your data on solid-state storage, you might not need to consider caching and tiering; but if your data center is like the majority of data centers, most of your current application data is kept on some type of spinning hard disk drives.

With

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tiering for SSDs, the user decides what data to place on the SSD and when to place it there. Tiering can be performed manually or with automated tiering software on the host or in the storage controller. Tiering is all about moving specific hot data to the SSD tier at the right time and moving it back to the slower disk tiers (again, at the right time). If tiering is performed manually, then the administrator must observe the I/O activity over time and decide when to move certain files or data. You would have to manually track the number of accesses of every file on all your systems and then decide when to move files to and from SSDs based on those accesses. For systems of any size, this would be an impossible task to do manually, so automated tiering software would be required. With automated tiering software, the file and data accesses are tracked automatically and data movement occurs at a scheduled time based on user-defined policies. Tiering only benefits the apps whose data is moved to the faster tier, but the performance boost is immediate and significant. Automated tiering solutions are a good choice if you have several applications you believe need the performance boost but you can’t or don’t want to decide -- or you don’t have the time to prove -- which apps need the performance boost. If you only had one application that could benefit from tiering, you wouldn’t need automated tiering software. But most data centers have dozens, hundreds or maybe even thousands of applications that could benefit from higher performance.

Solid-state caching

Another approach is SSD caching. Caching for SSDs is determined by host software or the storage controller, but it places a copy of the data into the SSD cache without moving the data from its original location that’s known to users and applications. Caching is relatively simple to manage because nearly all the decisions are made by the caching software or controller. Caching benefits any application whose data is considered “hot” within the scope of data accessible to the cache, but the performance improvement is a bit more gradual, increasing as more data is placed into the cache. This gradual performance improvement is called “warm-up” or “ramp-up,” and it can occur over minutes or hours, depending on the implementation and number of I/O operations occurring. Caching can be read-only or for both reads and writes, depending on the implementation. Caching with SSDs follows many of the same caching algorithms used for memory caching or even caches inside of processors. Some SSD caching solutions will not only cache the obvious hot data, but may pre-fetch adjacent data the caching software believes might become hot based on the I/O patterns observed. Most caching solutions let the admin decide which files or volumes are eligible for the cache performance boost, so you can exclude certain data from clogging the cache. If you believe that most or all of your applications would benefit from a performance boost, you should consider SSD caching.

With tiering and caching, SSDs can be added to the configurations to allow more capacity for the performance boost. For either of these solutions, you’ll have to figure out how much SSD capacity is need to make a difference. Many environments seem to need as little as 3% or as much as 10% of the total disk storage capacity in SSD technology to get a significant performance boost.

This was first published in March 2012

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