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DDR 3 / DDR4 NVDIMM Frequently Asked Questions (FAQs)

For additional information, contact dram@vikingtechnology.com

What is an NVDIMM?

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A Non-Volatile DIMM (NVDIMM) is a memory module that resides on the DDR DRAM channel & is persistent. NVDIMMs are built with both DRAM memory (volatile) and Flash (non-volatile) memory. Under normal power conditions NVDIMM operates exactly like a regular DRAM module; however, it differs from a standard DDR Memory Module, because it has integrated data movement logic that will transfer the data between the DRAM and Flash Memory during SAVE or RESTORE events.

During a power failure or system crash, the NVDIMM module is powered via a supercapacitor pack, thus the data contained within the DRAM once transferred to the Flash, is safe and can be considered persistent.

Does NVDIMM modules work like a Standard JEDEC DIMM?

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Yes, NVDIMM will operate just like a standard JEDEC DDR3 ECC Registered DIMM. It will continue to do so until it is enabled/instructed to store the volatile (DRAM) memory into the non-volatile (Flash) memory.

Why use NVDIMMs?

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APPLICATION PERFORMANCE & REBUILD TIME

NVDIMMs enable system memory to be persistent (Non-Volatile) in the event of power failure or system crash. By having this persistence, applications can run at far higher speeds - I/O performance in a host of applications, including storage and database acceleration are dramatically improved.

Additionally, there is a significant value to applications that are sensitive to down-time (OLTP, Financial institutions etc). In the event of power failure without NVDIMMs a typical environment would have the server & storage power be held up by UPS or generators for enough time to transfer the critical data safely into a NAS or SAN – this can take many minutes or even hours to complete, likewise the “rebuild time” upon power being restored. If NVDIMMs were integrated, the data is saved in seconds & upon power being restored, as soon as the server is rebooted, the data is immediately available.

Are NVDIMMs the same mechanical size as a JEDEC standard DIMM?

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Yes, NVDIMMs meets the mechanical dimensions defined by the JEDEC MO-269 specifications for a DDR3 DIMM module. Meeting the height, width and length of 133.35mm long x 30mm high x 7.55mm max width, respectively. The primary difference is that the NVDIMM has a cable to the supercapacitor power pack.

How do I integrate NVDIMMs into my system? Wouldn’t a special motherboard, CPU, and OS support be needed?

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Yes, NVDIMM must be used in an “NVDIMM” enabled server / platform. There are servers with NVDIMM support that are now available in the market, such as SuperMicro. If needed, Viking will work directly with our customer or customer’s development partner to successfully integrate the solution and provide technical and validation support on the BIOS and OS software.

Do I need to modify my OS, BIOS or Software?

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It depends upon the system. Some Intel Sandy Bridge Asyncronous DRAM Refresh (ADR) enabled systems will have the necessary BIOS for simple NVDIMM integration & complete functionality. All other systems will require BIOS modification. Viking will supply BIOS code modules and a porting guide to an OEM and/or ODM for AMI and Phoenix code bases. The Intel Jasper Forest and Atom S12x9 processors also have ADR support.

ADR - Asynchronous DRAM Refresh. Definition & what it does?

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ADR = Asynchronous DRAM Refresh, which is one of the methods employed in servers to flush pending write data into NVDIMMs during power failure or system crash.

ADR is a hardware trigger mechanism (an ADR pin on the DIMM edge), which, when triggered operates the NVDIMMs in self refresh mode. Based on Early A/C Power Failure Detection (from the power supply), an ADR enabled system will flush the write buffer, place the DRAM (NVDIMM) into self-refresh mode and allow the NVDIMM to perform a SAVE.

Note: ADR does NOT protect processor caches.

Viking Technology, being the leader in NVDIMM technology, has enabled an alternate method to trigger NVDIMMs which DOES protect CPU caches - See below for NMI Trigger

NMI Trigger, A method other than ADR to preserve data & trigger an NVDIMM SAVE.

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The NMI trigger allows for increased system performance, because CPU caches do not need to be turned off. The primary limitation of an ADR system is that it cannot protect processor caches. The NMI trigger method, allows the system to run with CPU caches turned on & will protect them in the event of a power failure.

How it works: The NMI trigger, calls an "NMI Handler" (software) which instructs the system to perform housekeeping functions; specifically CPU & Write Buffer flush.

Once cache and buffer flush is captured in the NVDIMM (takes approx 5ms) the NMI Handler places the NVDIMM into self-refresh mode and allows the NVDIMM to isolate from the host & perform a SAVE.

Where can I use NVDIMM?

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They must be integrated into an NVDIMM enabled platform. NVDIMMs resides in the DDR DIMM slots & can be accessed as main system memory or DRAM based storage.

What is the cost of an NVDIMM (price)?

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Contact Viking for pricing information at sales@vikingtechnology.com.

Will DDR4 NVDIMMs be available for next generation servers?

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Yes, Viking will be delivering DDR4 NVDIMMs to OEMs and the wider x86 eco-system - supporting the launch of next generation platforms (i.e Intel Haswell / Grantley)

Can I use any standard motherboard when using NVDIMM?

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No, the motherboard must have the necessary hardware support, such as ADR. Additionally, BIOS is required to detect NVDIMMs on boot up.

Why should I use Viking over other competitive solutions?

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Viking holds the industry NVDIMM technology leadership position. For many years Viking has been pioneering NVDIMM architecture and instrumental in driving the eco-system. Customers can rely on our experience and knowledgebase to simplify system design and integration of NVDIMMs. If TTM (time-to-market) is important, contact Viking Technology.

How and when does the NVDIMM module “SAVE” the data, making it persistent?

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When any one of the follow triggering events occur:

  • ADR signal drives a dedicated pin on the NVDIMM
  • Non maskable interrupt (NMI) Host initiated software command via I2C
  • A host initiated save via CKE signal
  • User configurable voltage level detection

the following sequence will occur:

  • The NVDIMM is isolated from the host
  • The DRAM data (including ECC) is transferred to the integrated Flash SSD, where it will safely reside until power is restored

For more information, please contact Viking at sales@vikingtechnology.com

How does the NVDIMM RESTORE the data from Flash back into the DRAM?

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Upon power-up, the data is restored from Flash back to into DRAM under BIOS control.

NVDIMM is only a portion of my total memory, how can I be sure that my system uses it for the data that needs to be persistent?

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The modified BIOS identifies the NVDIMM, rather than standard volatile DIMM. NVDIMMs can be addressed as a block device or as byte addressable memory. The memory map in the BIOS contains the memory addresses for the NVDIMM. Viking also provides a Memory Allocation Tool (MAT) that can simplify this task for programmers.

For more information, please contact Viking at sales@vikingtechnology.com

Can this NVDIMM have a RAM disk mounted and appear as a storage device?

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Yes. A RAM disk can be mapped over the NVDIMM. Please contact a Viking [email link] for directions on how to make NVDIMM appear to the host as a DRAM based SSD storage operating at speeds >10 GBytes/sec.

For more information, refer to RAM Disk, or RAM Drive

How do I restore the data to the DRAM if it needs to be available to the system during boot-up?

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The BIOS changes accommodate the Memory setup and recovery of the data.

What documentation is available for the NVDIMMs?

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You may find all Non-NDA related documents here: Arxcis-NV

For more detailed documentation and NDA sensitive materials, please contact Viking at sales@vikingtechnology.com

Does the host isolation mechanism add latency or SI issues?

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No

What happens to NVDIMMs on a normal power down? Is data backed up?

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Yes, upon reboot the host has the option to return DRAM to the state it was in prior to shutdown.

Can I mix NVDIMM with other DIMMs in the same system?

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Yes, but not in the same memory channel. If interleaving of the NVDIMMs is desired, there must be identical matching NVDIMM configurations in the channels that are interleaved. Exactly the same rules that apply to standard memory integration, apply to NVDIMMs.

Does Viking provide OS and application support?

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Yes, Viking can assist in providing needed OS support and application interfaces.

What applications are best suited for NVDIMMs?

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An NVDIMM is extremely well suited to applications that derive benefit from high performance and are sensitive to down time in the event of power failures or system crashes. Storage appliances, RAID cache, IMDB (In Memory Database), Metadata Servers storing indexes and OLTP (On Line Transaction Processing).

What benefit does NVDIMM provide if I am using SSD’s?

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NVDIMM are the perfect complement to a storage solution which already includes NAND Flash SSD. Used in conjunction with intelligent caching or tiering software, NVDIMMs acts as the write cache with far higher data rates & unlimited writes.

How do I use NVDIMM as a SSD cache?

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Intelligent caching software can enable NVDIMM as an SSD cache.

Can NVDIMMs provide instant on?

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Yes, the NVDIMMs can be used to enable an Instant On environment.

What if the server has a UPS and generators?

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An NVDIMM has its own power source and thus does not rely on UPS or generators to provide protection. UPS power supplies have been known to be unreliable and generators can run out of fuel, especially during disaster scenarios (earthquake, tsunami, hurricane, flood etc).

The NVDIMM saves the data to its integrated flash in seconds, without having to overload and hold up an entire NAS/SAN on which to dump the critical data.

Is checkpointing required?

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No, checkpoint is required as the data in the NVDIMM is reliable across power cycles.

What if there is only a brown-out?

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Brown-out saves can be aborted if needed. NVDIMMs can overcome multiple power glitches without losing protected data.

 

 

 

 

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