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November 25, 2013

Cray Cluster Connect (C3) Lustre Storage for Linux

Cray’s expert storage solutions are now available for popular x86 Linux clusters.  Cray Cluster Connect (C3) offers a complete Lustre storage solution for x86 Linux. C3 brings Supercomputing-class scalability to data- and I/O-hungry Linux clusters.

Cray’s approach to I/O optimization builds on holistic system expertise developed across the entire I/O stack, from applications down to storage.  Most storage vendors have expertise in a single specialized area (typically block or file storage). Cray’s expertise spans three interdependent disciplines—compute, networking, and storage—coming together to form adaptive yet massively scalable storage solutions.

Cray optimizes I/O through:

  1. Application workload profiling:  ensuring the I/O pattern is well characterized for optimal performance
  2. End-to-end system architectures:  all aspects of the system – compute, networking, and storage – are optimized for applications
  3. I/O testing and qualification at scale:  Cray pre-qualifies and extensively tests systems against a wide variety of I/O characteristics to simulate user I/O patterns.

Cray storage solutions are well suited to data hungry supercomputers and x86 Linux clusters.  Cray works proactively with customers to understand the application and I/O requirements.  “Cray makes sure the storage solution meets the customer’s requirements, “ says Mark Swan, principal performance engineer at Cray.  “If a customer’s workloads are not taking full advantage of available bandwidth, simply adding hardware or software is a Band-Aid. However, I have seen far too many customer workloads that do not perform the kinds of optimal I/O that would take advantage of the file system’s capabilities and that has nothing to do with fast or slow zones.”

Through Cray Cluster Connect (C3), Cray delivers complete Lustre storage solutions for popular x86 Linux clusters.  Customers choose their storage platform (Cray Sonexion, DDN SFA, or NetApp E-Series) and Cray optimizes the I/O and throughput.   Unlike conventional storage solution providers, Cray is able to optimize the I/O up the entire stack, from the storage up to the client.

“Cray configures systems to be extremely flexible from a purely I/O perspective,” says senior Cray engineer, John Kaitschuck. “We can configure as much capacity and I/O bandwidth as needed by a customer for a given application and couple that with a properly configured compute capability to achieve the desired I/O-to-compute balance for a given application.”

The type of I/O and application often dictates the network and storage design. “By proper analysis of the workload profile and configuration of the required associated capacity and bandwidth, Cray is able to optimally scale I/O as a customer’s needs grow,” adds Kaitschuck.

Workloads often fight for bandwidth—and I/O contention can take many forms.  “Cray storage architectures provide multiple pathways for data so that there is no single point of failure and no single point of contention,” says Swan.  “We also devise techniques so that I/O contention in one part of the file system does not interfere with other parts of the file system.  These techniques not only isolate failures but also isolate areas of contention from affecting the entire workload.”

“Cray is continually developing utilities to analyze the I/O path,” says Steve Woods, a senior practice leader in Cray’s storage division.  “Infiniband monitoring ensures there are no errors that might affect the performance of the network and to ensure the fabric operates at its anticipated bandwidth.”

“This testing includes a wide variety of I/O characteristics,” says Woods.  “Our tests simulate user I/O patterns. This testing is constantly evolving because of changes in hardware as it relates to disk drives, arrays, servers, and even the network interconnect technologies. Not only are various combinations of hardware are tested but in addition the various levels of software are also tested to insure there are no performance regressions associated with the different layers of software.”

Optimizing the I/O system is often related to improper tuning.  Tuning can be related to clients, networks, and storage.  This may be as simple as increasing certain buffers or balancing parameters for caching or command sequence to disk. In the case of routed I/O, like LNET routing in Lustre, various parameters may need tuning to handle peak small data floods or large streaming of data.”

Cray’s solutions ensure “full performance access” to the I/O subsystem, minimizing bottlenecks in the architecture, says Woods.  “This work includes analyzing the performance of all components of the IO subsystem—from LUNs to controllers to servers to networks across routers (if required) and to the clients. Part of the analysis includes testing and turning the software stack”, he added.

Cray also offers its own scalable storage line, Cray Sonexion.  Sonexion scales I/O bandwidth in lock-step with storage capacity.   The basic unit of storage in Sonexion—including performance and capacity—is the Scalable Storage Unit (SSU).  An SSU combines high capacity, high density storage with two all-active embedded controllers serving Lustre performance.   For customers that need to add more capacity than performance, Cray offers Expansion Storage Units (ESUs).

In cases where customers need to optimize capacity or performance for a given workload, the Lustre™ File System by Cray (CLFS) can be utilized with DDN SFA or NetApp E-Series storage.  Lustre solutions by Cray are installed separately on x86 servers and provides a high degree of configuration flexibility.

Cray storage solutions help customers utilize the right storage and get results faster.  The Cray storage solution at the NCSA Blue Waters provides an example of I/O optimization at the petascale, for diverse applications. “During the Blue Waters acceptance period,” according to Swan, “Cray worked with the PSDNS turbulence application.  By analyzing its check-pointing methods, Cray optimized the I/O path to reduce check-pointing and application runtime.”

Since Cray fully tests and qualifies all solutions, users obtain an optimal experience, where I/O can be scaled as needed, and systems work as specified.   The product of the all the hard work done by Cray is that systems operate predictably.  By giving customers choice in a storage platform, the ROI matches the customers’ requirements.  In petascale scenarios, Cray reduces the storage footprint by up to 50%–and scales I/O to 1TB/s in a single file system.

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