NVMe Performance and Drivers
This graphic illustrates the difference between SCSI and NVMe in the Linux storage stack. NVMe reduces latency overhead by more than 50% by removing the request queue and SCSI translation layer. By utilizing the block-layer driver, NVMe saves 10,000 CPU cycles, and dedicating these extra CPU cycles to applications or other host processes will provide a performance advantage.
There will be an accompanying evolution of the software stack, and operating systems, to take advantage of the enhanced performance. Like the transition to fully utilizing multiple CPU cores after their debut, this will not occur overnight. NVMe drivers will hasten the transition by simplifying and standardizing software interaction with the storage stack.
The standardized Windows StorNVMe.sys driver follows the StorPort model. StorPort is an optimized library of hardened drivers that scales from servers to tablets. StorNVMe also supports interrupt coalescing for optimum latency performance and is NUMA-optimized.
This graph compares the performance of NVMe against SATA and SAS devices, but also compares a flash-based NVMe drive to a RAM-based NVMe drive. The advantages of moving beyond flash for ultra-high-performance applications will likely spawn a new set of DRAM-based products to address the high-performance segment in the interim before next generation non-volatile memories.
Initial performance comparisons from Intel tout a 2x performance over 12Gb/s SAS and 4-6x the performance of SATA SSDs. We will be conducting tests to compare the speed of the P3700 against an array of leading 6Gb/s SATA and 12Gb/s SAS SSDs, look to these pages soon for a full report.
Database and virtualization workloads will benefit tremendously from NVMe architecture. NVMe provides native atomic I/O size affinity for databases and matches natural application I/O granularity.
The multi-core nature of NVMe queueing is well suited for virtualization workloads and its multi-threaded performance requirements. Servicing the I/O from submission to completion on the same core occupied by the application thread will significantly increase performance, especially once software engineers begin to tap the possibilities of NVMe performance.
The comparison between NVMe and SATA SSDs are unavoidable, and rightly so. Replacing 6 SSDs with one PCIe SSD is a performance win, but the benefits of PCIe SSDs extend beyond the normal bandwidth and IOPS measurements.
Switching to a PCIe SSD eliminates several SSDs and an HBA or RAID adaptor. There are also peripheral advantages of reduced cabling and complexity. Another compelling use-case is in micro-server designs, where the enhanced performance density and capacity of an NVMe solution will facilitate smaller designs.
NVMe includes comprehensive end-to-end data protection (T10 DIF and DIX compliant), security and encryption capabilities (TCG), robust error correcting, and management capabilities (SMBus and I2C). Support for I/O virtualization architectures, such as SR-IOV, is also included.
Competing with SAS functionality required the development of similar enterprise-class features, such as Multi-Path I/O, namespace sharing, enhanced reset capabilities, and a reservation mechanism compatible with SCSI reservations. These features are baked into revision 1.1, and increased power management capabilities will be included in 1.2.
Autonomous power management provides low power states, similar to DEVSLP, in client applications. The NVMe implementation is autonomous, meaning the device does not have to power back up to receive commands to enter lower sleep states.
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