SSD, or solid-state disk, is a term that gets overused when we talk about solid-state storage. SSD is incorrectly applied to seemingly everything related to memory-based storage. In fact, any time I'm writing about memory-based storage I still refer to SSD first since it is the more common search term, but really the global use of SSD is inaccurate and we really should be using SSS, or solid-state storage.
SSS is a general term that is more applicable because memory-based storage can come in a variety of configurations. SSD is a very specific term that should be limited to memory-based storage that happens to be in a hard drive form factor. The advantage of SSD, of course, is that it, for the most part, can be installed in anything that formerly accepted a hard drive. If you want to upgrade the hard drive on your laptop or server, you can pull out the hard drive and replace it with an SSD.
SSD technology is also the path that many storage systems manufacturers have chosen to quickly deliver memory-based storage to their customers. They can use their existing storage shelves that used to hold hard drives and now place SSD into them. There are issues with integrating SSD into legacy architectures as we detail in our article "SSD in Legacy Storage Systems," which include that the shelf or the controller architecture may not be able to sustain the performance capabilities of a whole shelf full of SSD. In essence memory-based storage acts as a bottleneck exposer.
This performance concern has lead to the growth of a wide range of options in the SSS market. There are PCIe-based SSS devices. They eliminate many of the bottleneck variables by removing the latency caused by the storage network. There are challenges sharing PCIe SSS across multiple servers. which applications like clustering and virtualization require.
Another option is to use SSS appliance-based systems that put memory-based storage into an appliance and make it available like any other block device attached to the storage network via fibre or 10-Gbps Ethernet. These systems often don't use SSD form factor, but instead use memory modules or custom boards so that greater density can be achieved. Shared SSS appliances of course have to deal with the storage network as well as developing their own internal switching architectures so that packaging of the appliance itself does not become an inhibitor to performance.
As we will discuss in our upcoming webcast "Understanding SSD Performance," there is more to performance than how fast the devices are. How SSS is packaged will be one of the key factors in determining performance. We have made the device, because it is memory, so fast that it now exposes all the other weaknesses in the performance chain and it is up to suppliers to develop technology that removes those bottlenecks.
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