SSDs Are All About Latency

Nearly every storage manufacturer has been articulating a solid state disk (SSD) strategy in the past two quarters. EMC, HP, IBM, HDS, NetApp, and Compellent are all set to add the capability to their offering. Some are doing so today, while others are still in the strategy mapping process.What most of them agree on is that SSDs can be a game changer, with the potential performance improvements of 30X when compared with mechanical drives. A key issue for them and you to understand is latency.

First, what is latency? Also called response time or wait time, in storage terms it is the amount of time between a request being made and that request being fulfilled. A user example would be the amount of time it takes from you launching your word processor to you being able to start typing.

For most applications, standard mechanical hard drives fulfill these requests fast enough that this response time isn't even noticed, but sticking with the word processing example, what if as you started to type your novel, you had to wait two seconds between the time you press a letter and the time that you could press the next letter? That would get annoying real fast and it would cost you time and probably money. Your important revenue generating application treats response time the same way.

So what makes the latency of various storage systems different? In the past it had all been about the speed of the drives. Everything else in the storage system was able to respond faster than the drives so the focus became making the drives faster by using higher RPM drives, array groups with a high drive count, short-stroking those drives, wide striping those drives and increasing the number of application servers for improved parallelism.

SSDs change that focus, the speed of the drive is no longer the issue. SSDs change the latency focus on the storage system itself and away from the drive. Manufacturers will need to change how these SSD shelves are addressed or create standalone systems like those from Texas Memory Systems, Solid Data Systems, and Violin Memory.

In our next entry we will take a deeper dive into the impact on storage systems as a result of zero latency at the drive level.

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George Crump is founder of Storage Switzerland, an analyst firm focused on the virtualization and storage marketplaces. It provides strategic consulting and analysis to storage users, suppliers, and integrators. An industry veteran of more than 25 years, Crump has held engineering and sales positions at various IT industry manufacturers and integrators. Prior to Storage Switzerland, he was CTO at one of the nation's largest integrators.