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Fine print: Dell bod tells us the details of Fluid Cache for SAN

It's not just for Dell's own servers, says marketer

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Fluid Cache for SAN is Dell’s technology to integrate server PCIe flash cards and networked SAN storage. We talked to Bob Fine, director of product marketing at Compellent to find out more about how it works.

El Reg: Is Compellent's Storage Center (Data Progression functionality) loading data into the connected server's PCIe flash cache?

Bob Fine: Loading data into the cache is initiated by the application, rather than Data Progression. Data Progression ensures that data no longer needed at the cache layer is moved to the most efficient storage tier. Compellent’s Enterprise Manager (management tool) provides our customers with a single interface to provide end-to-end management of both the SAN and server cache layer.

El Reg: How many servers with their flash caches can be supported by Storage Center?

Bob Fine: The architecture for Fluid Cache supports 8 servers at initial release. These servers can be a combination of both Dell and non-Dell servers. The Dell servers supported are representative of current and [coming] servers [to be] released in the next few months. Each server participating in the cluster will use a PCI express bus connected with hot pluggable MLC-based flash drives.

El Reg: Does each server get its flash cache loaded with unique data or do all the caches in the cluster get the same data?

Bob Fine: Each node can access data that is in the cache cluster via a low latency connection. This ensures that we do not keep multiple copies of the data in cache and can fully utilise the cache capacity. With write back caching we mirror data between nodes to ensure high availability and reliability.

El Reg: How often are a server's flash cache contents updated?

Bob Fine: Contents are updated continuously based on application demand.

El Reg: Do the servers write data to the cache and, if so, how soon is that written to the backend Compellent SAN?

Bob Fine: Fluid Cache has the ability to cache data in the cache pool. The contents of a write are mirrored to another node via low latency connection to ensure HA (high-avaulability) and reliability. Fluid Cache will flush data to the array continuously, and in the event of a replay (snapshot).

El Reg: Is the application speed acceleration such that it is part of the reason or the whole reason that Dell does not have a ground-up designed all-flash array?

Bob Fine: Interesting question. What benefits are there compared to a ground-up design all-flash array? Dell offers customers multiple options depending on their performance needs since real world needs can be vastly different. Our broad approach is best. As you know, we offer all-flash arrays with both Compellent and EqualLogic in systems that can be all-flash or also support disc, as well, offering customers greater flexibility for now and the future.

Also, with our unique Compellent approach, we can provide all-flash for the price of 15K disk. Our research from our launch this past fall showed that the Dell Compellent all-flash solution can be up to 75 per cent less expensive compared to other all-flash storage solutions from traditional vendors by automatically tiering across SLC and MLC SSDs. At the same time it provides the performance of competitors’ all-flash arrays yet with better economics. This choice addresses customers that have a range of high performance needs.

With our new [Storage Centre 6.5] release, we are adding compression as well. This provides high performance, with great economics for our flash tier and disk tier. The best of both worlds.


Supported flash cards are:

  • Micron M420P SSDs (700GB/1.4TB>
  • Dell’s Express Flash PCIe SLC SSDs (175GB/350GB - branded Micron product we think
  • Express Flash PCIe SSD MLC NVMe SSDs (400GB/800GB/1.6TB - sourced from Samsung)

Analyst outfit Stifel Nicolaus' MD, Aaron Rakers, points out that Dell's website does not list Fusion-io's ioDRive2 PCIe flash cards as being supported despite them being an option for Dell's PowerEdge servers.

Fluid Cache for SAN supports host servers running Red Hat Enterprise Linux 6.3 and 6.4, Novell SUSE Linux Enterprise Server 11 (service pack 3) and vSphere ESXi 5.,5 – but not, so far, Windows.

The Compellent SC8000 controller is supported, along with the SC220 array.

The minimum cluster size with Fluid Cache for SAN is three nodes. The software is perpetually licensed on a per-node scheme. Get a Fluid Cache for SAN spec sheet here (pdf).

The Vulture's view is that the performance improvements in servers using Fluid Cache for SAN hooked up to Compellent arrays - detailed here - are impressive enough to suggest that having those servers hooked up to a brand new all-flash array without using the Fluid Cache technology might be insignificant. Especially when an all-flash Compellent array could be used with Fluid Cache for SAN, and there is no need to separately obtain and manage a new supplier's all-flash array.

The Dell base could well look very favourably on the Fluid Cache for SAN idea as a way to boost server performance within their existing Dell infrastructure. ®

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