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NVMe: PCIe card vs U.2 and M.2

We talk NVMe form factor choices – add-in card vs U.2. vs M.2 – and their uses, for primary storage or cache, with Server StorageIO founder and analyst Greg Schulz

Non-volatile memory express (NVMe) is a peripheral component interconnect express (PCIe)-based standard protocol that can allow solid state storage to work to its full potential by hugely increasing drive connectivity performance.

NVMe can be deployed via PCIe form factors that include add-in cards (AiC), M.2 and U.2.

Methods to allow NVMe’s fast access performance are being developed for use across storage networks and fabrics, but for the time being NVMe is mostly a replacement for serial advanced technology attachment (SATA) and serial-attached SCSI (SAS) drives in servers or possibly storage arrays.

Here, Antony Adshead, storage editor at Computer Weekly, talks to Greg Schulz, founder and senior consulting analyst of independent IT advisory consultancy firm Server StorageIO about NVMe deployment options.

Antony Adshead: Why use a U.2 slot when you could use the PCIe AiC? 

Greg Schulz: Simple. Your server or storage system may be PCIe slot constrained yet have more available U.2 slots. There are U.2 drives from various suppliers including Intel and Micro, as well as servers from Dell, Intel and Lenovo among many others.

Adshead: Why and when would you use an NVMe M.2 device? 

Schulz: As a local read/write cache, or perhaps a boot and system device on servers or appliances that have M.2 slots. Many servers and smaller workstations including Intel NUC support M.2. Likewise, there are M.2 devices from many different suppliers including Micron and Samsung, among others.

More on NVMe

Adshead: Where and why would you use NVMe PCIe AiC? 

Schulz: Whenever you can and if you have enough PCIe slots of the proper form factor, including the number of lanes – for example x1, x4, x8, x16 – to support a particular card.

Adshead: Can you mix and match different types of NVMe devices in the same server or appliance?

Schulz: As long as the physical server and its software (BIOS/UEFI, operating system, hypervisors, drivers) support it, then yes. Most server and appliance suppliers support PCIe NVMe AiCs, but you need to pay attention to precise form factor. You should also verify operating system and hypervisor device driver support. PCIe NVMe AiCs are available from Dell, Intel, Micron and many other suppliers.

Adshead: Does having M.2. mean you have NVMe?

Schulz: That depends. Some systems implement M.2 with SATA, while others support NVMe. Read the fine print or ask for clarification.

Adshead: Who should we keep an eye on in the NVMe ecosystem?

Schulz: Suppliers to look out for include E8, Enmotus (micro-tiering software), Excelero, Magnotics, Mellanox, Microsemi, Microsoft (Windows Server 2016 S2D, ReFS), NVM Express trade groups (for example, nvmexpress.org), Seagate, VMware (there is a native NVMe driver available as part of vSphere ESXi) and WD/Sandisk.

This was last published in February 2017

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U.2 or M.2 even if they are PCI-e standard-specification, will they perform the same as PCI-e add-in card? It may help in extreme speed apps, fraud detection, web personalization, video streaming, genomic sequencing, HPC, database activities.
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@RajaKT good question, a U.2 NVMe is using PCIe x4 (e.g. G3) similar to some AiC that are also x4 G3. Depending on the implementation, those x4 PCIe lanes on the U.2 connector simply pass back to the main PCIe bus via a riser or other interface unless they have a native on the motherboard trace. Where you can expect to see an increased performance with AiC are those that are x8 or x16 mechanical (e.g. physical slot) and electrical (e.g. active lanes). Likewise the card and its sw/fw have to be able to process the faster speeds, same with the U.2 (or M.2) for that matter. Long story short, have seen some x4 AiC perform similar to U.2 and vise versa, otoh, have seen x8 or better be much faster. Also on M.2, make sure that it is in fact NVMe M.2 and not a SATA/AHCI M.2 ;)
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