ANX 1500 Technical Overview
The ANX 1500 is so much more than a cache appliance; it is an NFS throughput accelerator. Almost anyone can put SSDs and DRAM into a server chassis, but most system designers can’t match Alacritech’s ability to move data in and out of caches with both speed and maximum efficiency.
The ANX 1500 addresses the real business problems associated with NAS scalability. Achieving a record setting SPECsfs2008* NFSv3 overall response time (ORT) of .92ms was no accident, Alacritech’s TCP Offload technology is a significant element of the system design, but isn’t the entire story. The integration of a single-stack processing model, NFS data acceleration integrated into the underlying Sahara hardware, a sophisticated cache management system, an extremely low latency write-through model designed to ensure data consistency with the NAS, and a significant amount of software to bring it all together in a compact, highly scalable design, is what really defines the product. Alacritech was in the best position to harness the potential of SSD technology to deliver exceptional throughput and minimal latency, with minimal burden on the customer’s compute, storage, and networking infrastructure.
What’s In the ANX 1500 NFS Throughput Acceleration Appliance?
The ANX 1500 is equipped with 20 200GB SSDs (4TB capacity) and 48GB of DRAM. Using a LRU model, the most active data is stored in DRAM and as requests for the data subside, data is moved to SSDs; then, assuming fresher data is competing for space, data is ejected. When a request is made for data stored on SSDs, data is moved back from the SSDs into DRAM—based upon an initiated DMA—and out to the requesting clients. Alacritech’s technology quickly moves data with minimal processor intervention. With years of experience designing TCP/IP Offload Accelerators, Alacritech has mastered the art and science of moving data with minimal server resource consumption. When Alacritech designed the ANX, the objective was to create a performance acceleration layer to sit alongside existing NAS, making use of on-board cache and Alacritech’s acceleration technology—which resulted in greater processor, memory, and networking efficiencies. With the ANX taking on the task of satisfying client read and most NFS metadata requests, these efficiencies directly benefit the supported NAS resulting in overall higher performance and scalability. The ANX 1500 makes use of two Alacritech 10GbE Network Accelerators. This technology represents Alacritech’s six generation design. While the design of these products has historically been focused exclusively on TCP/IP Offload, Alacritech made some notable additions to the accelerator logic executed in its Sahara on-board silicon and developed a fair amount of new software, both optimized for NFS acceleration.
Alacritech’s Dynamic TCP Offload is a “stateful” offload model. The host operating system, with its own network stack, transfers connection state information to a network accelerator (NIC) designed to assume the state from the host and process TCP/IP. After a connection is passed, the network accelerator examines the header information of incoming frames and moves the associated payload with very little host CPU intervention. The ANX 1500 leverages this base technology plus additional enhancements. What enhancements? First, Alacritech’s software executes a single-stack processing model. No interrupts or context switches take place in the data path. Second, Alacritech added logic embedded in its Sahara custom silicon to buffer and read NFS RPC headers and transport the corresponding NFS event to an assigned processor core. Each of the 16 processor cores is capable of processing NFS requests, generating NFS replies, and when necessary, forwarding requests in the event of a cache miss. This virtually eliminates processor stalls associated with spinlocks and processor cache thrashing. Third, Alacritech built a custom Cache Manager that tracks what is in each cache location and for how long, in addition to providing housekeeping functions. Fourth and last, the ANX 1500 was designed to pass writes through to the NAS with single-digit microsecond latency. The data is held by the ANX in DRAM, but not made available to satisfy a subsequent read until an acknowledgement is received from the NAS.
*SPECsfs is a trademark of the Standard Performance Evaluation Corporation. Test results for Alacritech NFS Throughput Acceleration Appliance can be found at:www.spec.org/sfs2008/results/sfs2008nfs.html.