Flash Storage Architecture: What's Available and Why It Matters

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Flash Storage Architecture: What's Available and Why It Matters-5

Caching Hybrid

Caching-hybrid systems have an architecture in which flash is used as a cache for a pool of disks, either as a read and write cache or solely as a read cache. While caching-hybrid systems do deliver better performance than post-process-tiering systems, they come with significant drawbacks. Because flash is being used as a cache, rather than as storage media, the cache does not contribute to the overall capacity of the system, making these caching-hybrid systems more expensive than tiering systems in terms of cost per gigabyte of raw capacity. In addition, systems that use flash only to cache reads have to employ DRAM to serialize writes that are made directly to spinning media. This strategy works only with very small working sets. If the working set is large, write performance slows to the pace of disk drives, lowering overall system performance.

Moreover, as innovations in both flash and other solid-state storage media continue, hybrid systems that use multiple (two or more) solid-state media types will soon become possible. Systems that employ a caching-hybrid architecture can't benefit from these innovations, since when two types of flash are used there is very little performance difference between the cache and the pooled media. Therefore caching-hybrid systems using multiple solid state media types only secure marginal performance benefits from caching, despite a significant increase in cost. Also many caching hybrids do not support dedupe, and when dedupe is supported it must be disabled for volumes that are performance sensitive.

Everyone in the storage market is excited about flash. As well they should be. Flash can deliver much better performance than spinning disks. In addition, the cost of flash media is starting to come down to a level where all enterprises should consider adding flash-based storage to their enterprise storage infrastructure.

Yet amidst all this excitement there is also confusion. In particular, as vendors introduce a variety of all-flash and hybrid-flash storage systems, many storage administrators are confused as to the differences between the systems, as well as the benefits and drawbacks of each of them. Almost all current products in the flash storage landscape can be broken down into four different types of system architectures – all-flash, post-process tiering hybrid, caching hybrid, and continuous tiering hybrid – each with its own unique characteristics.

By comparing flash storage architectures side by side, storage administrators can better understand what flash architectures – and by extension what flash products – make the most sense for their particular set of applications. In doing so, they are likely to find that while flash has improved enterprise storage system performance, until recently storage system architectures have failed to keep up with media and other technology advancements, and fully leveraged these technologies to deliver better performance while minimizing data storage costs.

In this slideshow, Jacob Cherian, vice president of product strategy at Reduxio, takes a closer look at the four flash storage architectures currently on the market.

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