NVMe (Non-Volatile Memory Express) Overview and Primer – Part I
Learn more about Non-volatile memory express (NVMe), like what it is, and performance impact.
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This is the first in a five-part miniseries providing a primer and overview of NVMe. View companion posts and more material at www.thenvmeplace.com.
Defining NVM Express (NVMe)
Non-Volatile Memory (NVM) includes persistent memory such as NAND flash and other forms Solid State Devices (SSD). NVM express (NVMe) is a new server storage I/P protocol alternative to AHCI/SATA and the SCSI protocol used by Serial Attached SCSI (SAS). Note that the name NVMe is owned and managed by the industry trade group for NVM Express is (www.nvmexpress.org).
The key question with NVMe is not if, rather when, where, why, how and with what will it appear in your data center or server storage I/O data infrastructure. This is a companion to material that I have on my microsite www.thenvmeplace.com that provides an overview of NVMe, as well as helps to discuss some of the questions about NVMe.
Main features of NVMe include among others:
- Lower latency due to improving drivers and increased queues (and queue sizes)
- Lower CPU used to handle larger number of I/Os (more CPU available for useful work)
- Higher I/O activity rates (IOPs) to boost productivity unlock value of fast flash and NVM
- Bandwidth improvements leveraging various fast PCIe interface and available lanes
- Dual-pathing of devices like what is available with dual-path SAS devices
- Unlock the value of more cores per processor socket and software threads (productivity)
- Various packaging options, deployment scenarios and configuration options
- Appears as a standard storage device on most operating systems
- Plug-play with in-box drivers on many popular operating systems and hypervisors
Why NVMe for Server Storage I/O?
NVMe has been designed from the ground up for accessing fast storage including flash SSD leveraging PCI Express (PCIe). The benefits include lower latency, improved concurrency, increased performance and the ability to unleash a lot more of the potential of modern multi-core modern processors.
Figure 1 shows common server I/O connectivity including PCIe, SAS, SATA and NVMe.
NVMe, leveraging PCIe, enables modern applications to reach their full potential. NVMe is one of those rare, generational protocol upgrades that comes around every couple of decades to help unlock the full performance value of servers and storage. NVMe does need new drivers, but once in place, it plugs and plays seamlessly with existing tools, software and user experiences. Likewise, many of those drivers are now in the box (e.g. ship with) for popular operating systems and hypervisors.
While SATA and SAS provided enough bandwidth for HDDs and some SSD uses, more performance is needed. NVMe near-term does not replace SAS or SATA they can and will coexist for years to come enabling different tiers of server storage I/O performance.
NVMe unlocks the potential of flash-based storage by allowing up to 65,536 (64K) queues each with 64K commands per queue. SATA allowed for only one command queue capable of holding 32 commands per queue and SAS supports a queue with 64K command entries. As a result, the storage IO capabilities of flash can now be fed across PCIe much faster to enable modern multi-core processors to complete more useful work in less time.
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