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Structuring Storage with RAID, Cache and Tiering Print
September 2014

This article introduces caching and tiering technologies to further enhance storage performance or to reduce overall storage costs.

Our first generation of storage systems employed RAID levels 1, 10, 5, 6, 50, and 60 - all of which are capable techniques to achieve data redundancy and performance using multiple disks.  The underlying performance is still restricted by the individual disk members that make up the arrays. Disks come in different types, sizes, performance capabilities and prices; at present we have affordable 6TB SATA disks for bulk storage that are slow and cheap, 1.2TB SAS disks for mainstream storage that are faster and still affordable, or 800GB SSD disks that are extremely fast but also rather expensive.

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Figure 1: Three individual RAID volumes (800GB, 2.4TB, 12TB) with varying levels of performance


How do we build and manage storage to achieve an optimum level of performance, capacity and cost with these disks? Enter a new generation of storage systems with caching and tiering technology. While our first generation of systems employed RAID only, our second-generation of storage allowed solid state drives (SSDs) to be configured as cache. Caching stores the most frequently-accessed data in the cache pool. This "hot" data is then read from the cache instead of from spinning hard disk drives, thus improving read performance many fold.

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Figure 2: Single RAID volume of 12TB with Caching for acceleration


Our latest generation of storage introduces fully redundant write caching support, hybrid SSD cache, and tiering functionality. Write caching support introduces the performance enhancing caching technique to a much broader set of application workloads. Hybrid SSD caching allows SSDs to be partitioned into both a cache and a storage device for an OS or data that requires continuous, fast, and low-latency access - thus allowing finer control or configurability. Last but not least, the tiering functionality provides optimised use of disk performance and capacity by assigning disks and data into different tiers of performance - Tier 0 can be fast SSD only storage, while Tier 1 is bulk storage for infrequently accessed data.

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Figure 3: Single Tiered volume of 15.2TB for optimal performance


Essentially tiering offers an optimised structure of storage by allowing us the ability to assign performance to the data that matters most (automatically without user intervention). The system, with an intelligent policy engine, will gather statistical I/O information to make decisions on data priority. "Hot" data will be placed on the fastest storage media while "Cold" data will be placed on slower media.

Contact our team for further information or assistance with your next storage solution.