VFCache obviously works well where goosing performance over current levels (EMC states 50 percent improvement in response time and 210 percent improvement in throughput) provides an advantage for enterprises , including OLTP (online transaction processing systems) and business analytics. Naturally, your mileage may vary as performance improvement will vary depending on the workload characteristics. Given the critical nature of the former to enterprises of every sort and the growing use of the latter across multiple industries, VFCache should be a valuable addition to EMC's arsenal.
Note that flash cache is not just physical hardware; to maximize benefits, it has to be powered by sophisticated software for processes including examining I/Os. EMC's VFCache uses a lightweight I/O inspection technology (meaning that the CPU resources are impacted very little which EMC claims is a competitive advantage) that leverages some of the capabilities of the company's well-tested PowerPath software. Caching and cache management logic is also critical and EMC has had tons of experience in this area (as every storage array has a layer of cache that EMC has successfully polished and refined throughout the years).
One very interesting VFCache capability is called split card, which allows part of the flash cache to be treated strictly as cache and part as if it were DAS (direct-attached storage). That means that part of the data in the cache changes dynamically as different data is required for performance reasons to be put there. However, part of the cache could be used as if it were DAS to store ephemeral-like temporary databases in an SQL Server environment. (which means that this portion of cache is not subject to the algorithms that are responsible for moving data to and from that part of cache that acts as true cache). This capability gives IT more flexible choices in managing the overall cache.
As noted above, the second place flash cache is most often located is in the server-network. The reason for this is simple: Server-based cache is dedicated to a particular server (which means that each server requires its own committed PCIe flash cache card). While that may be optimal for some critical applications, there can also be a problem establishing the correct sizing of the flash cache on a server. If the application requires less than the minimum cache size to accelerate performance, the underutilized space is wasted as it cannot be shared with other servers; if the application requires more flash cache than can be provided as a maximum at the server level, the application suffers from not being able to achieve all the performance that it could have otherwise obtained.
Now this problem can occur even when application I/O demands are predictable over a very narrow band over time, i.e. more or less static. However, the problem can be further exacerbated when application I/O varies dynamically for a known period of time (such as the significant boost in OLTP during the December holiday season) or as the result of a special event (such as a product launch or promotion). Sharing cache in the network may not solve all the problems but it provides better workload optimization than non-shared server cache.
So it should come as no surprise that EMC has pre-announced (with Q2 2012 initial availability) a scalable server-network-based flash appliance that will couple together multiple VFCache cards. Now, the surprise is not what EMC is announcing, but that it pre-announced at all given that it does have a history of not doing public technology previews. One can assume a simple rationale in that by doing so the company's is alerting potential customers so they can incorporate EMC's direction into their planning process. While VFCache may prove to be very beneficial, wise IT organizations recognize that implementing new technologies into their IT infrastructure requires serious due diligence, which takes some time. And, oh by the way, EMC's pre-announcement also blunts potential arguments by server-network flash cache vendors.
What does this do to the competitive market? Well, some might say that EMC is validating the SSD market. Actually, while the announcement is a strong reaffirmation of the value of SSD, the market was already validated by EMC's solid success in these areas.
