Plexistor nonvolatile storage software gets wrapped in hardware

Plexistor unveils Persistent Memory over Fabric hardware bundles. The startup's storage-defined memory platform presents DRAM and nonvolatile storage in a single namespace.

Plexistor is adding a hardware dimension to its software-defined memory product, which converges server memory and flash as nonvolatile storage, and it is scheduled for release in 2017.

The new product, Persistent Memory over Fabric Brick (PMoF Brick), bundles Plexistor software-defined memory (SDM) with 2U Supermicro servers and flash-based nonvolatile dual inline memory module (NVDIMM) cards by Micron Technology Inc. Each brick will have 25 TB to 50 TB of raw capacity and is designed to serve a single rack.

The PMoF Brick architecture allows persistent memory to be disaggregated and shared across multiple servers. Primary use cases include big data analytics and high-performance computing, particularly Cassandra, Couchbase and other NoSQL database applications.

PMoF Brick has been qualified to run on Hewlett Packard Enterprise's Persistent Memory ProLiant DL380 Gen 9 hardware, as well as Supermicro X10 servers.

Plexistor CEO Sharon Azulai said the PMoF bundle makes it easier for customers to consume Plexistor SDM.

"Deploying nonvolatile memory like NVDIMMs is complicated," Azulai said. "It means you [have to] buy a machine that can support NVDIMMs or something like 3D XPoint. We took a different approach. We came up with a concept to place persistent memory in a single box, and enabling our file storage system to use it as a remote persistent memory."

Applications see SDM capacity as memory or nonvolatile storage

We came up with a concept to place persistent memory in a single box, and enabling our file storage system to use it as a remote persistent memory.
Sharon AzulaiCEO, Plexistor

Plexistor SDM presents DRAM and persistent storage within a single namespace. Users think they are accessing files locally, when in fact they are being sent across the wire. The persistent storage devices can be flash-based NVDIMMs or commercially available solid-state drives.

The architecture allows an application to consume pooled resources based on its need. Depending on the application, SDM exposes the capacity as either memory or storage. Conventional applications see SDM as a file system, whereas an in-memory database application sees it as byte-addressable nonvolatile storage.

SDM is a server-side installation that bypasses the operating system software stack and instead talks directly to a physical memory device. It supports clones and snapshots. Compression and data deduplication are on the vendor's product roadmap.

Plexistor PMoF Brick is conceptually similar to NVMe over Fabric (NVMe-oF)  architectures. The difference is NVMe-oF uses iSCSI semantics to transfer commands for block storage. Plexistor's fabric-connected bricks use memory semantics to allocate memory ranges.

"When Plexistor says they're sharing persistent memory, they're kind of skating the issue a little bit. It's more like near memory than persistent memory [due to] the way it's treated by the system. But it enables very high performance and low-latency nonvolatile storage," said Marc Staimer, a founding analyst at Dragon Slayer Consulting in Beaverton, Ore.

Is a Plexistor PMoF Brick more than just packaging?

Azulai describes PMoF Brick as "a centralized box that can have lots of persistent memory types.

"We have the ability to manage two different fields -- nonvolatile memory and nonvolatile storage -- and present them as unified capacity or unified storage to the servers. It lets you use SDM and achieve persistence over the wire" for in-memory databases, Azulai said.

The standard PMoF Brick configuration is a primary tier of DRAM with a secondary tier of flash storage, including solid-state drives or NVMe flash devices. Plexistor mirrors data from servers to the subsystem memory using Remote Direct Memory Access (RDMA) across 100 Gigabit Ethernet switching.

Staimer said PMoF Brick will deliver similar latency as NVMe-oF, but with less cost and higher scalability.

"Not too many IT shops will open up their servers and add persistent memory," he said. "Too many things could go wrong -- and probably will. Plexistor eliminates that issue. You put in one of their boxes, connect it to a bunch of servers and get the same effect."

Azulai said pricing for the PMoF Brick has not been finalized. Proofs of concept are underway with about 15 customers.

Next Steps

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Outlining the issues when using in-memory databases

Netlist lays out new NVDIMM devices

Dig Deeper on All-flash arrays