Samiksha Jaiswal (Editor)

NVDIMM

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A Non-Volatile Dual In-line Memory Module (NVDIMM) is a random-access memory for computers. "Non-volatile" means that the memory retains its contents even when electrical power is removed either from an unexpected power loss, system crash, or normal shutdown. "Dual in-line" identifies the product as using the DIMM package. NVDIMMs improve application performance, data security, and system crash recovery time. They enhance SSD endurance and reliability.

Contents

"Non-volatile" products may use volatile memory during normal operation and dump the contents into non-volatile memory if the power fails, using an on-board backup power source. Volatile memory is faster than non-volatile; it is byte-addressable; and it can be written to arbitrarily, without concerns about wear and device lifespan. However, including a second memory to achieve non-volatility (and the on-board backup power source) increases the product cost compared to volatile memory.

Types

There are two main types of NVDIMM cards:

  • NVDIMM-F devices achieve non-volatility using a flash memory. They may have a cache that presents a small amount of the device's contents to the computer as a volatile DIMM would, byte-addressable and just as fast. However, when the computer requests memory that is not in the cache, the device imposes a delay as new blocks are copied from flash into the cache. They have more capacity than typical DIMMs and can expand application memory to multiple terabytes. NVDIMM-F has been available since 2014.
  • NVDIMM-N is a device that presents a volatile memory to the computer like any other DIMM. A typical method of achieving non-volatility is to copy information to a separate non-volatile memory, such as flash, invisibly to the computer, even in the case that the computer's power fails.

    • As of November 2012, most NVDIMMs used NAND flash as the non-volatile memory. Emerging memory technologies aim to achieve NVDIMM without a cache or two separate memories. Intel and Micron have announced use of the 3D XPoint non-volatile memory technology in NVDIMMs, and Sony and Viking Technology have announced an NVDIMM-N product based on the ReRAM technology.

    Backup power

    NVDIMMs evolved from the BBU (battery backed up) DIMM, which used a backup battery to sustain power to a volatile memory for up to 72 hours. However, batteries are disfavored in computer components because they have a limited lifespan, they may be regarded as hazardous waste, and they contain heavy metals which violate RoHS compliance.

    When the module includes non-volatile memory, on-board backup power is only required for a short time after the computer's power fails. Therefore, modern NVDIMMs use supercapacitors to store energy.

    Interface

    A few server vendors, such as Supermicro, still make products using the DDR3 interface to the computer, but standardization work in 2014 and 2015, such as at JEDEC and ACPI, was based on the DDR4 interface.

    Uses

    The BBU DIMM was originally designed for use as the cache of RAID HBAs (host bus adapters) or systems, to enable data in the cache to survive a power failure. NVDIMMs have moved beyond RAID applications into fast storage appliances or in-memory processing for the data center and cloud computing.

    References

    NVDIMM Wikipedia
    (Text) CC BY-SA