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Server PCIe flash cache trend catching on with storage vendors

EMC heads list of major storage vendors jumping on the server-based PCIe flash cache trend to reduce latency and supply higher bandwidth for read-heavy, I/O-intensive applications.

Server-based PCI Express (PCIe) flash cards have made their mark for primary data storage, and they’re starting to attract increased attention for caching now that EMC Corp. and other major vendors are jumping on the flash cache trend.

Caching at the application server offers the advantage of reduced latency by eliminating the network hop to the storage array, and directly-connected PCIe offers higher bandwidth than Fibre Channel, Ethernet, SAS and InfiniBand.

Dennis Martin, president of Arvada, Colo.-based Demartek LLC, thinks server-based flash caching will trend upward.

“It’s simple to manage. It’s an easy way to get a performance bump. And you don’t have to change your back-end storage at all,” said Martin.

Martin noted that read-intensive applications such as database, Web and file servers are especially “cache friendly.” IT shops in need of a performance boost will find several server-based cache products in the market and more on the way, he said.

Before EMC jumped in, host-based software flash cache vendors included

Fusion-io, LSI Inc., STEC, Nevex Virtual Technologies, OCZ Technology Group Inc., SanDisk Corp. and VeloBit Inc. Most of these sell PCIe cards, as well as software, although Nevex and VeloBit are software-only vendors.

Fusion-io Inc., the key player offering PCIe flash cards for primary storage, sells two software caching applications -- ioTurbine for virtual environments and directCache  for physical servers. 

“A caching model can make sense in some of those environments where you have so much data that not all of it’s being actively used,” said Gary Orenstein, vice president of products at Fusion-io.

The bulk of Fusion-io’s business since 2008 has come from selling server-based PCIe flash cards for primary storage, largely through its partnerships with Dell Inc., Hewlett-Packard Co., IBM Corp. and Super Micro Computer Inc. Orenstein stresses the importance of giving customers the option not to have a SAN array, which he views chiefly as a vehicle for “capacity and long-term retention.”

In contrast, Barry Ader, senior director of product marketing and management for EMC’s flash business unit, pointed to the importance of data protection, reliability and high availability with networked storage arrays in connection with VFCache, the company’s new server-based PCIe flash cache that was formerly known as Project Lightning.

The server flash cache trend is expanding to a new dimension as major vendors such as EMC and NetApp Inc. pledge software to better integrate the server flash with their backend arrays. Several storage vendors declined comment on their potential host-based flash cache plans.

“EMC’s the first one to do this as a storage vendor,” Martin said, “and you can bet other storage guys will do the equivalent because they want to make the sale for this card, and they’d rather have you buy it from them rather than from somebody else.”

With the February introduction of VFCache, EMC outlined plans to more deeply integrate the product with its storage management technologies and Fully Automated Storage Tiering (FAST) architecture. EMC also previewed its Project Thunder server-networked flash appliance, which takes aim at I/O acceleration for multiple servers.

“Obviously as EMC moves forward, they’ll have their special sauce working best with EMC arrays,” said Stuart Miniman, principal research contributor for Wikibon, a community-focused research and analyst firm based in Marlborough, Mass.

Unlike EMC, NetApp currently sells flash cache only as part of its storage arrays. The company claims about 40% of systems are purchased with its Flash Cache in a virtual storage tier configuration. Flash Cache is now a standard feature in NetApp’s high-end FAS 6240 and FAS 6280 systems.

But, at last year’s USENIX-sponsored File and Storage Technologies in San Jose, Calif., NetApp unveiled a project code named Mercury for “host-side flash caching.” This year, during a February earnings call, NetApp CEO Tom Georgens noted the company’s goal of bringing data stored in host-based flash “into our data management methodology” for backup, replication and deduplication through a software component.

“The software is where the intelligence resides, and integration with storage systems, storage I/O stacks and other mechanisms is how these solutions will differentiate themselves over time,” Russ Fellows, a senior partner at Boulder, Colo.-based Evaluator Group Inc., wrote in an email to

EMC’s VFCache -- the first server-based cache released by a major storage vendor --combines a PCIe flash card from Micron or LSI and software that sits in the I/O path to determine if a piece of requested data resides on the PCIe card or solely in the backend storage system. The I/O filter driver software installs on the server operating system.

VFCache is a “write-through” cache, so initial data writes go from an application to the storage array. The PCIe flash cache card populates asynchronously to prevent application slowdown. The 300 GB PCIe card typically fills, or warms up, in 30 to 60 minutes for an application such as an Oracle Corp. database, according to Ader.

Although VFCache works with any server and external storage, Ader acknowledged that he doesn’t expect vendors such as HP and IBM to sell the product. He said EMC’s direct sales force and sales channel will sell VFCache as an extension to the storage sale, similar to the model in use with EMC’s server-based PowerPath multipathing software.

“Basically, if it touches storage, they want a part of it.,” Marc Staimer, president of Dragon Slayer Consulting in Beaverton, Ore., said of EMC. “They want to be able to manage it. They want to be able to control it. They want to be able to sell it.”

Ray Lucchesi, founder and president of Silverton Consulting Inc. in Broomfield, Colo., said EMC thinks “flash will be everywhere in the storage hierarchy, and as such, if there’s some advantage to be gained by having the control over the software at the server level, they want it.”

“Once they have this software in place and they enhance the software, it can be more effective with their storage,” Lucchesi said. “And if that’s the case, then they start locking in more and more of the whole path into EMC profit margin.”

One of the major limitations of server-based flash caches is that they work only in one server. Also, if the server hosts virtual machines (VMs), the software needs to work with key virtualization features such as VMware Inc.’s VMotion, which allows users to move VMs from one server to another. Vendors such as Fusion-io and OCZ already promote their support for VMotion as a product differentiator.

Demartek’s Martin said that will be the next issue for vendors to resolve.

“That’s not trivial, but it can be done. That’s the next thing you’re going to start seeing people talk about,” Martin said. “Certainly when EMC goes to Thunder or anybody else does anything that involves more than one server, you have to figure out how you’re going to move that data from the PCIe card in the one server into the PCIe card in the other server.”

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