Scott Drummonds on Virtualization

The Flash Storage Revolution: Part I


Six weeks ago I finally upgraded my MacBook to solid state storage.  The change in performance is so dramatic, to say the least.  I have been selling flash storage to EMC’s customers for over a year now and they have been loving it.  But I did not really get how valuable flash is until I saw it on my own laptop.

After this revolution of my own mind, I want to dedicate a few blog entries to the issue of solid state storage in the enterprise.  First I want to frame the problem that flash both solves and causes.  In the second entry I will introduce some of the theory behind flash sizing.  My last article will give you some very simple practical advice on how to use flash in your enterprise.

These entries lean heavily on a presentation EMC’s Denis Vilfort presented within EMC a few weeks ago.  I am providing a PDF version of that presentation on this blog for your own usage.

The fundamental problem that flash is solving is summarized in the following figure.

The speed of rotating disks is dictated by the time it takes the hard drive head reach data on the platter. These mechanisms–a spinning disk and a moving arm–are basically unchanged in the past many decades. Array performance has evolved through the introduction of DRAM cache, intelligent prefetch, clever file systems, and other techniques. But the metaphorical hands of all enterprise storage vendors were bound by the physics of spinning platters and actuating arms. While latencies in hard drive technologies have stuck in the milliseconds, solid state devices like CPU, memory, and flash have improved to microseconds and nanoseconds.

This huge chasm in performance between disk and memory increasingly devalued high performance servers. When storage becomes the bottleneck for a business application, the performance of a server becomes less important. VMware introduced the importance of capacity in server sizing by showing the world consolidation. But performance of data intensive applications was still dictated by storage.

The initial challenge of solid state disks (SSD) was their perceived high cost when compared to hard disks. I remember a couple years ago hearing EMC’s confused messaging around its enterprise flash disks (EFDs): “much more expensive but much, much faster”. Customers were left with a confusing, cost-benefit calculation to make a purchasing decision.

A year and a half ago that EMC started using a more clear message for flash: in some cases, it is actually cheaper than rotating disks. The key is to identify these use cases. This is best shown in the following figure.

Because of the exceptional improvement in latency, flash drives provide dramatically higher throughput on random access patterns than hard drives. When normalized by throughput–IOPS in the case of the above figure–flash storage is much cheaper than any hard drive.

But there is another angle to storage efficiency. Even “cheap” hard drive storage was never as cheap as people thought. When arrays aggregate striped disks to sum their maximum throughputs, utilization is low. Furthermore, in some performance environments hard drives were short stroked, which meant only a small, fast section of the platter was used so performance could be maximized. With low utilization and short stroking, hard drive efficiency is very low. This means the nominal cost of rotating disks is much worse than people realized.

The low cost of your hard drives depends on their high capacity utilization. But how can you drive high capacity utilization in an environment where you have a storage performance bottleneck? Obviously flash is the answer.

SSD storage can help you solve your utilization and efficiency problems with rotating disks. But this assumes that you and your storage can determine how much flash you need and how to use it. And that will be the subject of my next entry in this three part series.

4 Responses

Disk performance is only flat for latency, throughput is growing quite quickly. Also flash faces some significant challenges, as you shrink the cell size you decrease cell lifetime, MLC flash is already pretty abysmal so the situation after a few more process shrinks starts to look bleak unless some major breakthrough happens.

  • […] the previous entry on this ongoing series covering the flash storage revolution, I concluded that flash is now an essential part of enterprise storage. But its value proposition […]

  • […] Drummonds has a great series going on titled “The Flash Storage Revolution”. In part 1, Scott discussed why flash is so important in enterprise storage today; in part 2, Scott addressed […]

  • […] my three part series on flash I interchangeably used the terms “flash” and “SSD”. […]