Solutions like Fusion-io have been around for some time. Typically, these products surround NAND-based local storage solutions. Moving application components to NAND storage provides significant IO benefits. Server vendors have profited by selling rebranded Fusion-io products, such as:
Until the end of 2011, the solutions were presented as local storage. With the astronomical rise of virtualization into enterprise environments, the idea of local storage became blasphemy. Many of advantages of virtualization are realized through shared storage. Without going deep into the details, Fusion-io has developed a technique to turn server-side NAND-based storage devices into caching devices. Conceptually, the cache is a read-cache with write-passthrough. Using a filter driver in the guest OS, VMs can benefit from shared storage while taking advantage of locally available cache. Now storage vendors, like EMC and its Project Lightning/VFCache, are trying to play catch up.
Moving data from the storage device to the local server is packed full of benefits: microsecond access times, tens of thousands of IOPS, and so on. But, the bigger question becomes: How do storage vendors approach this new storage technique?
Storage design continues to be an extremely important component of enterprise architecture, but server-side caching may mean rethinking configuration. At first glance, it seems there should be fewer higher-performing disks in the storage infrastructure, as all of the performance is local to the server. Suddenly, populating storage arrays with high-capacity SATA disks sounds like a great cost savings. The storage array becomes truly purpose-built for capacity and performance is an afterthought.
However, hopefully before the storage admin pulls the trigger on replacing disks, they will realize some important truths about server cache technology:
The fact of the matter is that with server-side caching solutions, a properly designed storage environment will be critical to support instances where the cache cannot be used. The utopian dream of inexpensive high-capacity SATA disks in the array is far from a reality. Storage vendors should be able to take advantage of the server-side cache to enable their solutions as well as a well-balanced storage solution.
At the end of the day, storage vendors do not appear to have much to worry about with the server-side cache technology. A cache still requires an underlying storage environment to provide the actual data and functionality, and that needs to perform at peak levels to support noncache situations. Some design decisions may change slightly, but modern solutions are still necessary.
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