In this model, the appliance can support a number of filers, not just one, so it's both sharable and scalable. The intent is to provide cycles back to the NAS so it can do its job in delivering performance to applications and have its life extended.
The pros are simplicity and cost-effective performance. The cons include not being able to cache CIFS traffic today and the dependency on the back-end NAS to handle non-cacheable operations. If there are bottlenecks on the filer, such as too few drives with limited IOPS to handle a burst in un-cached reads, there could be a temporary spike in latency. But for many working sets in environments where many clients are accessing much of the same data, as the cache warms, this isn't an issue.
In summary, there are many flash products available in the market today. They are diverse enough to where they shouldn't all be put in a bucket labeled as flash storage. Hopefully this review of Flash solutions' architectural differences, benefits and shortcomings has helped illuminate the fact that more informed choices can be made.
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