UltraDIMM – Silverton Consulting

Dreaming of SCM but living with NVDIMMs…

Last months GreyBeards on Storage podcast was with Rob Peglar, CTO and Sr. VP of Symbolic IO. Most of the discussion was on their new storage product but what also got my interest is that they are developing their storage system using NVDIMM technologies.

In the past I would have called NVDIMMs NonVolatile RAM but with the latest incarnation it’s all packaged up in a single DIMM and has both NAND and DRAM on board. It looks a lot like 3D XPoint but without the wait.

The first time I saw similar technology was at SFD5 with Diablo Technologies and SANdisk, a Western Digital company (videos here and here). At that time they were calling them UltraDIMM and memory class storage. ULTRADIMMs had an onboard SSD and DRAM and they provided a sort of virtual memory (paged) access to the substantial (SSD) storage behind the DRAM page(s). I wrote two blog posts about UltraDIMM and MCS (called MCS, UltraDIMM and memory IO, the new path ahead part1 and part2).

NVDIMM defined

NVDIMMs are currently available today from Micron, Crucial, NetList, Viking, and probably others. With today’s NVDIMM there is no large SSD (like ULTRADIMMs, just backing flash) and the complete storage capacity is available from the DRAM in the NVDIMM. At power reset, the NVDIMM sort of acts like virtual memory paging in data from the flash until all the data is in DRAM.

NVDIMM hardware includes control logic, DRAM, NAND and SuperCAPs/Batteries together in one DIMM. DRAM is used for normal memory traffic but in the case of a power outage, the data from DRAM is offloaded onto the NAND in the NVDIMM using the SuperCAP/Battery to hold up the DRAM memory just long enough to transfer it to flash..

Th problem with good, old DRAM is that it is volatile, which means when power is gone so is your data. With NVDIMMs (3D XPoint and other new non-volatile storage class memories also share this characteristic), when power goes away your data is still available and persists across power outages.

For example, Micron offers an 8GB, JEDEC DDR4 compliant, 288-pin NVDIMM that has 8GB of DRAM and 16GB of SLC flash in a single DIMM. Depending on part, it has 14.9-16.2GB/s of bandwidth and 1866-2400 MT/s (million memory transfers/second). Roughly translating MT/s to IOPS, says with ~17GB/sec and at an 8KB block size, the device should be able to do ~2.1 MIO/s (million IO operations per second [never thought I would need an acronym for that]).

Another thing that makes NVDIMMs unique in the storage world is that they are byte addressable.

Hardware – check, Software?

SNIA has a NVM Programming (NVMP) Technical Working Group (TWG), which has been working to help adoption of the new technology. In addition to the NVMP TWG, there’s pmem.io, SANdisk’s NVMFS (2013 FMS paper, formerly known as DirectFS) and Intel’s pmfs (persistent memory file system) GitHub repository. Couldn’t find any GitHub for NVMFS but both pmem.io and pmfs are well along the development path for Linux.

The TWG identified a three prong approach to NVDIMM adoption: crawl, walk, run (see pmem.io blog post for more info).

The Crawl approach uses standard block and file system drivers on Linux to talk to a NVDIMM driver. This way has the benefit of being well tested, well known and widely available (except for the NVDIMM driver). The downside is that you have a full block IO or file IO stack in front of a device that can potentially do 2.1 MIO/s and it is likely to cause a lot of overhead reducing this potential significantly.
The Walk approach uses a persistent memory file system (pmfs?) to directly access the NVDIMM storage using memory mapped IO. The advantage here is that there’s absolutely no kernel code active during a NVDIMM data access. But building a file system or block store up around this may require some application level code.
The Run approach wasn’t described well in the blog post but it seems like SANdisk’s NVMFS approach which uses both standard NVMe SSDs and non-volatile memory to build a hybrid (NVDIMM-SSD) file system.

Symbolic IO as another run approach?

Symbolic IO computationally defined storage is intended to make use of NVDIMM technology and in the Store [update 12/16/16] appliance version has SSD storage as well in a hybrid NVDIMM-SSD run-like solution. The appliance has a full version of Linux SymCE which doesn’t use a file system or the PMEM library to access the data, it’s just byte addressable storage ~~with a PMEM file system embedded within~~ [update 12/16/16]. This means that applications can use standard Linux file APIs to (directly) reference NVDIMM and the backend SSD storage.

It’s computationally defined because they use compute power to symbolically transform the data reducing data footprint in NVDIMM and subsequently in the SSD backing tier. Checkout the podcast to learn more

I came away from the podcast thinking that NVDIMMs are more prevalent than I thought. So, that’s what prompted this post.

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Photo Credit(s): UltraDIMM photo taken by Ray at SFD5, Architecture picture from pmem.io blog post,

MCS, UltraDIMMs and memory IO, the new path ahead – part 2

Posted on June 24, 2014June 25, 2014 by Ray in Block Storage, DAS, data protection, SSD storage, Storage

In part 1 (see previous post here), we discussed the underlying technology for SanDisk‘s UltraDIMMs based on Diablo Technologies MCS hardware and software. IBM will be shipping UltraDIMMs in their high end servers later this year as their new eXFlash.

In this segment we will discuss what SanDisk has put on top of the Diablo Technology’s MCS to supply SSD storage.

SanDisk UltraDIMM SSD storage

In the UltraDIMM package, SanDisk supports 200 or 400GB of 19nm MLC NAND SSD storage that is accessed via SATA [corrected after this went out, Ed.] internally, but the main interface is the 1600MHz, DDR3 to the UltraDIMMs. As each UltraDIMM card plugs into any DDR3 memory slot you can potentially support multiples of these cards in a single server. I believe the maximum number is ~~7 UltraDIMMs, not sure if IBM supports this many~~ [corrected after this went out, Ed.] dependent on the number of memory slots in your server. IBM on their x3850 and x3950 can support up to 32 UltraDIMMs per server.

SanDisk uses their Guardian Technology to enhance NAND endurance beyond what’s possible with native NAND controllers. One of the things that Guardian Technology does is to vary the voltage used to program the NAND bits over the life of the bit cells/pages. So early on when the cell is fresh, they can use less voltage and as it ages they increase the voltage to insure that the bits are properly programmed. With other NAND controllers, using the same voltage across the whole NAND lifetime it will unduly stress the NAND bits early on and later as they age, it will be unable to program properly and will need to be flagged as bad. The NAND chips/bits are characterized so that SanDisk Guardian Technology can use an optimum voltage curve over the chips lifetime.

The UltraDIMMs also have powerloss protection. This means that any write to an UltraDIMM memory that’s been acknowledged to the server is guaranteed to have sufficient power to make it all the way to the SSD storage.

Another thing that MCS memory interface brings to the picture is Error Correction Circuitry (ECC). Data written to UltraDIMMs has ECC protection throughout the data path up from the server DRAM memory, through the DIMM socket, all the way to the SSD flash.

As discussed extensively in Part 1 of this post, access times for UltraDIMM storage is on the order 7µsec, which is ~7X faster than best of class PCIe Flash storage and a single UltraDIMM card is capable of sustaining 20GB/second of data throughput. I know of enterprise class storage systems that can’t do half that in throughput.

On the other hand, one problem with UltraDIMM storage is that they are not hot swappable. This is primarily a memory interface problem and not an UltraDIMM issue but nonetheless, you can’t swap an UltraDIMM module until the server is powered down. And who would want to do such a thing when the server is powered anyway?

SanDisk long history in NAND

As you can see from the three photos at right SanDisk seems to have been involved in flash/NAND technology innovation since the early 1990’s. At the time NOR and NAND were competing for almost the same market.

But sometime in the mid to late 1990’s NAND found a niche in consumer cameras and never looked back. Not sure where NOR marketis today but it’s a drop in the bucket compared to the NAND market

UltraDIMMs is just the latest platform to support NAND storage access. It happens to be one with blazingly fast access times and high IO parallelism, but in the end it just represents another way to obtain the benefits of NAND for IT customers.

Also, SanDisk’s commercial NAND (Memory Card) business seems to be very healthy. What with higher resolution photos/video/audio coming online over the next decade or so it doesn’t seem to be going away anytime soon.

SanDisk is in a new joint venture (JV) with Toshiba to produce 3D NAND flash. But in the mean time they are still using 2D flash for their current SSD storage. Toshiba and SanDisk in their current JV together manufacture about 1/2 the NAND bits in the world today.

The rest of SanDisk NAND business also seem to be doing well. And the aforementioned JV with Toshiba on 3D NAND looks positioned to take all of this NAND to the next level of density as well which should make all of us happy.

SanDisk acquiring FusionIO

SanDisk was in the news lately as they have recently filed to acquire FusionIO, a prominent and early PCIe flash supplier that in recent years has broadened their portfolio to include enterprise storage with their acquisition of NexGen storage (renamed IO Control).

When FusionIO IPO’d the stock sold at ~$19/share and SanDisk is purchasing the company in an all cash deal for $11.25/share almost a 40% reduction in share price in 3 years (June’11 IPO) – ouch. At IPO the company was valued at ~$2B, (some pundits said this was ~$1.5B, so there’s some debate on the original valuation). SanDisk is buying the company for ~$1.1B in cash. Any way you look at it, they paid significantly less than what the company was worth at IPO. Granted, it was valued at 41X earnings then and its recent stock price at $11.59 represents a 3.3P/E (ttm).

Not exactly certain what happened. Analysts seem to indicate that Apple and Facebook, FusionIO’s biggest customers were buying less FusionIO product. I also happen to think that the PCIe flash space has gotten pretty crowded over the last 3 years with entrants from Micron Technologies, Intel, LSI, Verident/Western Digital, and others.

In addition, for PCIe flash to broaden its market there’s a serious need to surround it with sophisticated caching software to enable a more general purpose IO solution (see Pernix Data, Proximal Data, and others). These general purpose, caching solutions have finally reached high levels of sophistication and just now are becoming more widely available.

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Originally, part 3 of this series was going to be on IBM’s release of the UltraDIMM technology as their new eXFlash. However, I am somewhat surprised not to see other vendors taking up the MCS/UltraDIMM technology but IBM may have a limited exclusivity to it.

The only other thing thats this interesting happening in solid state storage is HP’s Memristor Machine which is still a ways off.

Nonetheless, a new much faster memory card based SSD is hitting the market and if history is any indication, it won’t be long until the data storage world will sit up and take notice.

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MCS, UltraDIMMs and memory IO, the new path ahead – part 1

Posted on May 22, 2014 by Ray in Block Storage, DAS, SSD storage, Storage, Storage architecture, Storage performance

I was at Storage Field Day 5 (SFD5) last month and got a chance to talk with SanDisk and Diablo Technologies. It turns out that SanDisk’s UltraDIMM product is based on Diablo Technologies MCS hardware. So the two of them provided a pretty deep dive into the technology and where they want to go with it. Before we go any deeper the UltraDIMMs will be released to the field by IBM under the eXFlash name.

Diablo Technologies

The team at Diablo have been focusing on the x86 standard memory channel for a while now and lately have been trying out different sorts of technologies to connect as CPU memory. The first Memory Channel Storage (MCS) product converts Memory Channel IO to SATA IO. This allows any SATA device to be attached as memory and enjoy lightening fast, memory access times. Access times are clocked at 7µsec. Most PCIe Flash cards have an access latency at 50µsec or more, so this is 7X faster that PCIe Flash. They also claim the MCS is capable of 20GB/sec. I know enterprise class storage systems that can’t do that. Also, the MCS utilizes 2 memory channels.

Diablo delivers a chip (that converts MemIO to SATA IO) and software that provides a block IO access to the MCS device. Customers of MCS supply their own SATA flash storage device and presumably package it all together in a DIMM compatible card.

But the main problem is that the whole MCS chip and SATA IO flash device has to fit in the form factor of a DIMM. And cannot draw any more power than a memory device can draw, ~10-15W with its corresponding thermal load.

But this seems plenty for a small flash drive. The MCS is configured as a 4GB DDR3 DIMM. There is a requirement to patch the BIOS so that it doesn’t run diagnostic memory tests on the MCS device and their software needs to be loaded to access the device as a block device. I believe they currently support Linux O/S with more O/Ss on the way.

Diablo has looked at other applications for their technology including providing an Memory IO accessed Ethernet NIC was mentioned. But it seems flash storage would be a great first application of their technology. Not clear to me but SAS would also be something that could be done.

Whatever happens after NAND with the next generation semiconductor storage (see my The end of NAND is near post, it seems to me that accessing it as Memory IO would make an awful lot of sense. makes a lot of sense. Using MCS as the access channel would seem to be a logical next step.

Part 1 of this story is on Diablo Technologies, Part 2 will be on SanDisk and I am not sure but maybe there will be a Part 3 on IBM eXFlash. So stay tuned.

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